A permutation *p* of size *n* is an array such that every integer from 1 to *n* occurs exactly once in this array.

Let's call a permutation an almost identity permutation iff there exist at least *n* - *k* indices *i* (1 ≤ *i* ≤ *n*) such that *p*<sub class="lower-index">*i*</sub> = *i*.

Your task is to count the number of almost identity permutations for given numbers *n* and *k*.
The first line contains two integers *n* and *k* (4 ≤ *n* ≤ 1000, 1 ≤ *k* ≤ 4).
none
4 1
1
4 2
7
5 3
31
5 4
76
200 1
1
200 2
19901
200 3
2646701
200 4
584811251
400 1
1
400 2
79801
400 3
21253401
400 4
9477912501
600 1
1
600 2
179701
600 3
71820101
600 4
48187303751
800 1
1
800 2
319601
800 3
170346801
800 4
152620985001
1000 1
1
1000 2
499501
1000 3
332833501
1000 4
373086956251
4 4
24
from sys import stdin,stdout
import math
nmbr = lambda: int(input())
lst = lambda:list(map(int,input().split()))
def ncr(n,r):
    lim=min(r,n-r)
    num,den=5,1
    nn=dd=1
    for i in range(lim):
        nn*=num
        dd*=den
        num-=1
        den+=1
    return nn//dd
for _ in range(1):#nmbr():
    n,k=lst()
    dp=[0]*(1+n)
    dp[1]=0
    dp[2]=1
    for i in range(3,n+1):
        dp[i]=(i-1)*(dp[i-1]+dp[i-2])
    sm=p=0
    while p<=k:
        sm+=ncr(n,p)*dp[p]
        p+=1
    print(sm+1)