#include <bits/stdc++.h>
using namespace std;
using ll = long long;

size_t N;
ll K;
string S;
ll tot[100001];

void solve(){
    cin>>N>>K;
    cin>>S;

    size_t i=0,y=0,x;
    for(x=1;x<=N*10;++x){
        if(y==0) ++i,++y;
        tot[x]=i;
        y+=S[(x-1)%N]-'0'-1;
    }
    if(K<=(ll)N*10) {
        cout<<tot[K]<<endl;
        return;
    }
    ll diff=tot[N*8]-tot[N*7];
    ll a=(K/N)-7;
    cout<<tot[7*N+K%N]+a*diff<<endl;
}

int main(int argc, char** argv) {
    if(argc==1){
        ios::sync_with_stdio(0);
        cin.tie(0); 
    }
    string s;
    size_t i;
    for(i=0;i<(size_t)argc-1;++i){
        s+=argv[i+1]; s+='\n';
    }
    for(i=0;i<s.size();++i) ungetc(s[s.size()-1-i], stdin);
    solve();
    return 0;
}