This problem is different from the easy version. In this version Ujan makes at most 2n swaps. In addition, k ≤ 1000, n ≤ 50 and it is necessary to print swaps themselves. You can hack this problem if you solve it. But you can hack the previous problem only if you solve both problems.

After struggling and failing many times, Ujan decided to try to clean up his house again. He decided to get his strings in order first.

Ujan has two distinct strings s and t of length n consisting of only of lowercase English characters. He wants to make them equal. Since Ujan is lazy, he will perform the following operation at most 2n times: he takes two positions i and j (1 ≤ i,j ≤ n, the values i and j can be equal or different), and swaps the characters s_i and t_j.

Ujan's goal is to make the strings s and t equal. He does not need to minimize the number of performed operations: any sequence of operations of length 2n or shorter is suitable.

Input

The first line contains a single integer k (1 ≤ k ≤ 1000), the number of test cases.

For each of the test cases, the first line contains a single integer n (2 ≤ n ≤ 50), the length of the strings s and t. 

Each of the next two lines contains the strings s and t, each having length exactly n. The strings consist only of lowercase English letters. It is guaranteed that strings are different.

Output

For each test case, output "Yes" if Ujan can make the two strings equal with at most 2n operations and "No" otherwise. You can print each letter in any case (upper or lower).

In the case of "Yes" print m (1 ≤ m ≤ 2n) on the next line, where m is the number of swap operations to make the strings equal. Then print m lines, each line should contain two integers i, j (1 ≤ i, j ≤ n) meaning that Ujan swaps s_i and t_j during the corresponding operation. You do not need to minimize the number of operations. Any sequence of length not more than 2n is suitable.

Example

Input


4
5
souse
houhe
3
cat
dog
2
aa
az
3
abc
bca


Output


Yes
1
1 4
No
No
Yes
3
1 2
3 1
2 3
// Hash: iBgWfdRM7VUgjYAbzDCTwx/sgB0C2KLAhXwcJ2NlIvM=

import java.security.*;
import java.lang.annotation.*;
import java.nio.file.StandardOpenOption;
import java.util.stream.*;
import java.nio.file.Files;
import java.util.function.*;
import java.util.concurrent.*;
import java.util.*;
import java.nio.file.Paths;
import java.util.concurrent.atomic.AtomicReference;
import java.text.SimpleDateFormat;
import java.nio.charset.*;
import java.nio.file.Path;
import java.io.*;
import java.lang.reflect.*;
import java.text.DecimalFormat;
import java.math.*;



// Solution can be found in Submission.testCase(). psvm method can be found in Main.main(String[] args)
// Please note that the code isn't obfuscated; only compressed


public class Solution {
    public static void main(String[] args) throws Exception {
        Main.main(args);
    }
}


class Main{public static void main(String[]args)throws Exception{Class<?extends AbstractSubmission>clss=TaskB2.class;new TaskB2().runSubmission();}};







@ContestSubmission(ContestType.CODEFORCES)
@CacheVersion(0)
class TaskB2 extends AbstractSubmission {

	@Override
	public void testCase() {
		int k = sc.nextInt();
		sc.nextLine();
		outer: for (int i = 0; i < k; i++) {
			sc.nextLine();
			String s = sc.nextLine();
			String t = sc.nextLine();
			if ((s + t).chars().boxed().collect(Collectors.groupingBy(a -> a)).values().stream().anyMatch(a -> a.size() % 2 != 0)) {
				out.println("No");
				continue outer;
			}
			char[] S = s.toCharArray();
			char[] T = t.toCharArray();
			int N = S.length;
			out.println("Yes");
			out.println(2 * N - 2);
			for (int j = 0; j < S.length - 1; j++) {
				char c = S[j];
				int indxS = -1;
				for (int l = j+1; l < S.length; l++) {
					if (S[l] == c) {
						indxS = l; break;
					}
				}
				if (indxS >= 0) {
					swap(S, T, indxS, j);
					swap(S, T, j, j);

				} else {
					for (int l = j; l < S.length; l++) {
						if (T[l] == c) {
							indxS = l; break;
						}
					}
					swap(S, T, N-1, indxS);
					swap(S, T, N-1, j);
				}
			}
		}
	}

	public void swap(char[] S, char[] T, int i, int j) {
		out.println((i+1) + " " + (j+1));
		char tmp = S[i];
		S[i] = T[j];
		T[j] = tmp;
	}



	@Override
	public void init() {
		// Nothing here! Good for initializing look-up tables or cached values

		// Note that there could be multiple Problem instances running on different threads. Writing static variables
		// here (or anywhere else) could lead to race conditions! Use static initialization instead
	}











	// Set to TRUE to override default (which may both be true or false). Setting to FALSE has no effect

	/* DISABLE-CODE-COMPRESSION: TRUE */
	/* GLOBAL-DISABLE-CODE-COMPRESSION: DEFAULT */
	/* JAVA-6-COMPATIBILITY-MODE: DEFAULT */
	/* KEEP-UNUSED-DEPENDENCIES: DEFAULT */





	
};

abstract class AbstractSubmission{public FastScanner sc;public InputStream in;public PrintStream out;public PrintStream debug;public volatile double score=0;public volatile int testCaseCount=-1;public volatile int testCaseIndex;public volatile double progress=0;public void runSubmission(){runSubmission(false);}public void runSubmission(boolean debug){runSubmission(System.in,System.out,debug);}public void runSubmission(InputStream in,PrintStream out){runSubmission(in,out,false);}public void runSubmission(InputStream in,PrintStream out,boolean debug){runSubmission(in,out,debug?System.err:new VoidPrintStream());}public void runSubmission(InputStream in,OutputStream out,OutputStream debug){this.in=in;this.sc=new FastScanner(this.in);this.out=new PrintStream(out);this.debug=debug instanceof VoidOutputStream||debug instanceof VoidPrintStream?new VoidPrintStream():new DebugPrintStream(debug);ContestType type=getType();testCaseCount=type.testCaseCount;init();if(testCaseCount<=0){testCaseCount=sc.nextInt();sc.nextLine();}testCaseIndex=0;for(testCaseIndex=1;testCaseIndex<=testCaseCount;testCaseIndex++){progress=0;this.out.printf(type.caseString,testCaseIndex,testCaseCount);testCase();}}private class DebugPrintStream extends PrintStream{public DebugPrintStream(OutputStream debug){super(debug);}private Object conv(Object obj){if(obj instanceof byte[])return Arrays.toString((byte[])obj);else if(obj instanceof char[])return Arrays.toString((char[])obj);else if(obj instanceof short[])return Arrays.toString((short[])obj);else if(obj instanceof int[])return Arrays.toString((int[])obj);else if(obj instanceof long[])return Arrays.toString((long[])obj);else if(obj instanceof float[])return Arrays.toString((float[])obj);else if(obj instanceof double[])return Arrays.toString((double[])obj);else if(obj instanceof boolean[])return Arrays.toString((int[])obj);else if(obj instanceof Object[])return Arrays.deepToString((Object[])obj);else return obj;}public void print(Object obj){super.print(conv(obj));}public void println(Object obj){super.println(conv(obj));}}public ContestType getType(){return getType(getClass());}public static ContestType getType(Class<?extends AbstractSubmission>clss){return getAnnotation(clss).value();}private static ContestSubmission getAnnotation(Class<?extends AbstractSubmission>clss){if(!clss.isAnnotationPresent(ContestSubmission.class)){throw new RuntimeException("ContestSubmission annotation not present on class "+clss.getCanonicalName()+"!");}return clss.getAnnotation(ContestSubmission.class);}public abstract void testCase();public abstract void init();};

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)@interface CacheVersion{int value();};

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)@interface ContestSubmission{ContestType value();};

enum ContestType{PLAIN("",-1),ETH_JUDGE("",-1,null,false,false,6),GOOGLE("Case #%d: ",-1),GOOGLE_JAM("Case #%d: ",-1,"Solution.java",false,false,8),GOOGLE_JAM_INTERACTIVE("",-1,"Solution.java",false,false,8),FACEBOOK("Case #%d: ",-1),BLOOMBERG("",1,"Problem.java",false,false,8),SINGLE_TESTCASE("",1),OPTIMIZER("",1,null,false,false,8,true),HACKERRANK("",1,"Solution.java",false,false,8),CODEFORCES("",1,"Solution.java",false,false,8);public int testCaseCount;public String caseString;public String launcher;public boolean disableCompression;public boolean keepUnusedDependencies;public int javaVersion;public boolean isOptimizer;ContestType(String caseString,int testCaseCount,String launcher,boolean disableCompression,boolean keepUnusedDependencies,int javaVersion,boolean isOptimizer){this.caseString=caseString;this.testCaseCount=testCaseCount;this.launcher=launcher;this.disableCompression=disableCompression;this.javaVersion=javaVersion;this.keepUnusedDependencies=keepUnusedDependencies;this.isOptimizer=isOptimizer;}ContestType(String a1,int a2,String a3,boolean a4,boolean a5,int a6){this(a1,a2,a3,a4,a5,a6,false);}ContestType(String a1,int a2){this(a1,a2,null,false,false,8);}};

class FastScanner{private static String spaceDelimiters=" \t\n\r\f";private BufferedReader buffer;private StringTokenizer tokenizer;private InputStream stream;public FastScanner(InputStream stream){this.stream=stream;}public String nextLine(){if(this.buffer==null)this.buffer=new BufferedReader(new InputStreamReader(stream));while(tokenizer==null){try{tokenizer=new StringTokenizer(buffer.readLine()+"\n");}catch(IOException e){throw new RuntimeException("IO exception occured!",e);}}String res=tokenizer.nextToken("");if(!res.endsWith("\n"))throw new RuntimeException("waddaheq just heppenenened");res=res.substring(0,res.length()-1);if(res.contains("\n"))throw new RuntimeException("oke wat lamo");tokenizer=null;return res;}public String next(){if(this.buffer==null)this.buffer=new BufferedReader(new InputStreamReader(stream));while(tokenizer==null||!tokenizer.hasMoreTokens()){try{tokenizer=new StringTokenizer(buffer.readLine()+"\n");}catch(IOException e){throw new RuntimeException("IO exception occured!",e);}}return tokenizer.nextToken(spaceDelimiters);}public BigDecimal nextBigDecimal(){return new BigDecimal(next());}public BigInteger nextBigInteger(){return new BigInteger(next());}public int nextInt(){return Integer.parseInt(next());}public long nextLong(){return Long.parseLong(next());}public double nextDouble(){return Double.parseDouble(next());}};

@Retention(RetentionPolicy.SOURCE)@Target(ElementType.METHOD)@interface O{String value();};

@Target(ElementType.FIELD)@Retention(RetentionPolicy.RUNTIME)@interface Optimize{long imin()default 0;long imax()default 100;double fmin()default 0;double fmax()default 1;};

class VoidOutputStream extends OutputStream{public void write(int b){return;}public void write(byte b[]){return;}public void write(byte b[],int off,int len){return;}};

class VoidPrintStream extends PrintStream{public VoidPrintStream(){super(new VoidOutputStream());}public void write(int b){return;}public void print(char[]buf){return;}public void print(String s){return;}public void print(Object obj){return;}public void println(char[]buf){return;}public void println(String s){return;}public void println(Object obj){return;}public PrintStream format(Locale l,String s,Object...objs){return this;}public PrintStream format(String s,Object...objs){return this;}};