#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=1444999999994;
ll mod=1000000007;
int main(){
    ll n,k;
    cin >> n >> k;
    string s;
    cin >> s;
    s+=s;
    s+=s;
    s+=s;
    vector<vector<pair<ll,ll>>>db(n,vector<pair<ll,ll>>(40));
    for (ll i = 0; i < n; i++)
    {
        ll now=1;
        ll id=i;
        for (ll j = i; j < s.size(); j++)
        {
            now-=1;
            now+=s[j]-'0';
            if (now<=0)
            {
                break;
            }
            id=j+1;
        }
        if (id-i>n)
        {
            db[i][0]={i,inf};
        }else{
            db[i][0]={(id+1)%n,id-i+1};
        }
    }
    for (ll i = 1; i < 40; i++)
    {
        for (ll j = 0; j < n; j++)
        {
            db[j][i]={db[db[j][i-1].first][i-1].first,db[db[j][i-1].first][i-1].second+db[j][i-1].second};
        }
    }
    ll now=0;
    ll ans=0;
    vector<ll>two(42,1);
    for (ll i = 0; i < 40; i++)
    {
        two[i+1]=two[i]*2;
    }
    
    while (k>0)
    {
        for (ll i = 0; i < 40; i++)
        {
            if (db[now][i].second>k)
            {
                if (i==0)
                {
                    ans+=1;
                    k=0;
                    break;
                }else{
                    ans+=two[i-1];
                    k-=db[now][i-1].second;
                    now=db[now][i-1].first;
                    break;
                }
            }
        }
    }
    cout << ans << endl;
}