#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>

using namespace std;

int n,k,ans,atari,ataris,cost;
char s[51];

int main(){
    scanf("%d%d%s",&n,&k,s);
    
    for(int i=0;i<n;i++){
        if(atari){
            atari--;
        }
        else
            cost++;
        
        if(s[i%n]!='0'){
            atari+=s[i%n]-'0';
        }
    }
    
    ans=cost;
    ataris=atari;
    
    for(int i=1;i<k/n;i++){
        if(cost>atari){
            ans+=cost-atari;
            atari=0;
        }else{
            atari-=cost;
        }
        atari+=ataris;
    }
    
    if(k<n)
        ans=atari=0;
    
    for(int i=0;i<k%n;i++){
        if(atari)
            atari--;
        else
            ans++;
        
        if(s[i%n]!='0'){
            atari+=s[i%n]-'0';
        }
    }
    
    
    printf("%d\n",ans);
    
    return 0;
}