#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  int n,k;
  string s;
  cin>>n>>k>>s;
  int ans=0,cnt=0,res=0,pos=0;
  while(cnt<k){
    if(res>0) res--;
    else ans++;
    res+=s[pos]-'0';
    cnt++;
    pos++;
    if(pos>=n) pos-=n;
  }
  cout<<ans<<endl;
  return 0;
}