#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, K;
    string s;
    cin >> n >> K >> s;

    // int f = 0, b = 0;
    // for(int l = 0; l < 10; ++l){
    //     b = 0;
    //     for(int i = 0; i < n; ++i){
    //         if(f == 0)  b += 1;
    //         else    f -= 1;
    //         f += s[i] - '0';
    //     }
    //     cout << "free:" << f << ",buy:" << b << endl;
    // }
    
    int free = 0, buy = 0;
    for(int i = 0; i < n; ++i){
        if(free == 0)   buy += 1;
        else    free -= 1;
        free += s[i] - '0';
    }

    if(free == 0){
        int ans = K / n * buy;
        K %= n;
        if(K){
            for(int i = 0; i < n; ++i){
                if(free == 0)   ans += 1;
                else    free -= 1;
                if(--K == 0)    break;
                free += s[i] - '0';
            }
        }
        cout << ans << endl;
        return 0;
    }

    vector<P> dat(1, {free, buy});
    bool weight_loop = false;
    for(;;){
        buy = 0;
        for(int i = 0; i < n; ++i){
            if(free == 0)   buy += 1;
            else    free -= 1;
            free += s[i] - '0';
        }
        if(buy == 0)    break;
        if(dat.back() == make_pair(free, buy)){
            weight_loop = true;
            break;
        }
        dat.emplace_back(free, buy);
    }

    int sz = dat.size(), sum = 0;
    for(auto [f, b] : dat)  sum += b;
    int ans = 0;
    if(K >= sz * n){
        ans = sum;
        K -= sz * n;
        if(weight_loop){
            int m = K / n;
            ans += m * dat.back().second;
            K %= n;
            free = dat.back().first;
            if(K){
                for(int i = 0; i < n; ++i){
                    if(free == 0)   ans += 1;
                    else    free -= 1;
                    if(--K == 0)    break;
                    free += s[i] - '0';
                }
            }
        }
    }
    else{
        int m = K / n;
        for(int i = 0; i < m; ++i){
            ans += dat[i].second;
        }
        K %= n;
        if(K){
            free = dat[m].first;
            for(int i = 0; i < n; ++i){
                if(free == 0)   ans += 1;
                else    free -= 1;
                if(--K == 0)    break;
                free += s[i] - '0';
            }
        }
    }
    
    cout << ans << endl;

    return 0;
}