#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())
#define endl "\n"

ll n, k;
string s;

pair<ll, ll> f(ll cnt) {
    ll buy = 0, rem = 0;
    rep(i, cnt) {
        if (rem > 0) {
            rem--;
        }
        else {
            buy++;
        }
        rem += s[i] - '0';
    }
    return make_pair(buy, rem);
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    cin >> n >> k >> s;
    // 1周で済む場合
    if (n >= k) {
        cout << f(k).first << endl;
        return 0;
    }
    // 複数周する場合
    else {
        pair<ll, ll> p = f(n);
        if (p.first <= p.second) {
            cout << p.first << endl;
        }
        else {
            ll lp = k / n;
            ll ans = p.first + (lp - 1) * (p.first - p.second);
            pair<ll, ll> cp = f(k % n);
            ans += max(0LL, cp.first - p.second);
            cout << ans << endl;
        }
    }
    return 0;
}