Given is an integer N. Find the number of positive integers less than or equal to N that have an odd number of digits (in base ten without leading zeros).

Constraints

* 1 \leq N \leq 10^5

Input

Input is given from Standard Input in the following format:


N


Output

Print the number of positive integers less than or equal to N that have an odd number of digits.

Examples

Input

11


Output

9


Input

136


Output

46


Input

100000


Output

90909
#include <bits/stdc++.h>
using namespace std;
int n,ans,p=1,k;
signed main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        if(i>=p) p*=10,k++;
        if(k&1) ans++;
    }
    printf("%d",ans);
}
