#include <bits/stdc++.h>

#define show(x) cerr << #x << " = " << x << endl

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "sz=" << v.size() << "\n[";
    for (const auto& p : v) {
        os << p << ",";
    }
    os << "]\n";
    return os;
}

template <typename S, typename T>
ostream& operator<<(ostream& os, const pair<S, T>& p)
{
    os << "(" << p.first << "," << p.second
       << ")";
    return os;
}


constexpr ll MOD = 1e9 + 7;

template <typename T>
constexpr T INF = numeric_limits<T>::max() / 100;

ll N;
ll K;
string S;

ll sim(ll initial, ll icenum, vector<bool>& buy)
{
    ll rest = initial;
    buy.clear();
    buy.resize(icenum, false);
    for (ll i = 0; i < icenum; i++) {
        if (rest == 0) {
            buy[i] = true;
            rest += S[i] - '0';
        } else {
            buy[i] = false;
            rest--;
            rest += S[i] - '0';
        }
    }
    return rest;
}

int main()
{
    cin >> N >> K >> S;
    vector<bool> buy;

    if (K <= N) {
        sim(0, K, buy);
        ll num = 0;
        for (ll i = 0; i < K; i++) {
            if (buy[i]) {
                num++;
            }
        }
        cout << num << endl;
        return 0;
    }

    ll rest = sim(0, N, buy);
    ll buynum = 0;
    for (ll i = 0; i < N; i++) {
        if (buy[i]) {
            buynum++;
        }
    }
    if (rest >= N) {
        cout << buynum << endl;
        return 0;
    }

    sim(rest, N, buy);
    ll second = 0;
    for (ll i = 0; i < N; i++) {
        if (buy[i]) {
            second++;
        }
    }
    K -= N;
    const ll box = K / N;
    const ll res = K % N;
    buynum += box * second;
    sim(rest, res, buy);
    for (ll i = 0; i < res; i++) {
        if (buy[i]) {
            buynum++;
        }
    }
    cout << buynum << endl;

    return 0;
}