#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, t) for (ll i = s; i < (ll)(t); i++)
#define all(x) begin(x), end(x)

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

struct io_setup {
	io_setup() {
		ios::sync_with_stdio(false);
		cin.tie(nullptr);
		cout << fixed << setprecision(15);
	}
} io_setup;

void solve() {
	ll n, a;
	cin >> n >> a;
	string s;
	cin >> s;
	ll ans = 0;
	ll x = 1200;
	map<ll, pair<ll, ll>> mp;
	rep(lp, 0, 5) {
		if (mp.count(x)) {
			auto [nx, ad] = mp[x];
			if (a - ad > 0) {
				a -= ad;
				ans += n;
				x = nx;
				continue;
			}
		}
		int bx = x;
		ll ba = a;
		int flg = 0;
		rep(i, 0, n) {
			ans++;
			if (s[i] == '0') x--;
			else if (x < 1200) {
				a--;
				x++;
			} else flg = 1;
			if (a <= 0) {
				cout << ans << "\n";
				return;
			}
		}
		if (bx == x) {
			ll ad = (ba - a);
			ll tmp = (a - 1) / ad;
			a -= ad * tmp;
			ans += n * tmp;
		} else if (!flg) {
			ll ad = (ba - a);
			ll tmp = (a - 1) / ad;
			ll dx = (x - bx);
			a -= ad * tmp;
			ans += n * tmp;
			x += dx * tmp;
		} else mp[bx] = {x, ba - a};
	}
}

int main() {
	int t = 1;
	// cin >> t;
	while (t--) solve();
}