#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,atari1;
char s[51];

int main(){
    scanf("%d%d%s",&n,&k,s);
    
    for(int i=0;i<n;i++){
        if(atari)
            atari--;
        else
            ans++;
        
        if(s[i%n]!='0'){
            atari+=s[i%n]-'0';
        }
    }
    
    if(ans<atari){
        atari1=(n/k)*atari-(n/k-1)*(atari-ans);
    }else{
        atari1=atari;
    }
    
    ans=ans+(n/k-1)*max(ans-atari,0);
    
    if(k<n){
        atari1=0;
    }
    
    for(int i=0;i<k%n;i++){
        if(atari1)
            atari1--;
        else
            ans++;
        
        if(s[i%n]!='0'){
            atari1+=s[i%n]-'0';
        }
    }
    
    
    printf("%d\n",ans);
    
    return 0;
}