#include <iostream>
#include <iomanip>//小数点出力用
//cout << fixed << setprecision(10) << ans;
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <unordered_map>
using ll = long long;
using namespace std;
#define modPHash (ll)((1LL<<61)-1)
#define modP (ll)998244353
bool chkrng0idx(int pos, int sup) { return (0 <= pos && pos < sup); }
int clk4(int num) { return (num - 2) * (num % 2); }
void yn(bool tf) { cout << (tf ? "Yes\n" : "No\n"); }

int sim(string S, int bef) {
	int now = bef;
	for (int i = 0;i < S.size();i++) {
		if (S[i] == '0') {
			now--;
		}
		else {
			if (now < 1200) {
				now++;
			}
		}
	}
	return now;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	ll N, A;
	cin >> N >> A;
	string S;
	cin >> S;
	int delta = sim(S, -1010000) - (-1010000);
	int J = sim(S, 1200);
	int delta0 = J - 1200;
	if (delta < 0) {
		ll init = 0;
		int now = 1200;
		for (int i = 0;i < S.size();i++) {
			if (S[i] == '0') {
				now--;
			}
			else {
				if (now < 1200) {
					now++;
					init++;
				}
			}
		}
		if (A <= init) {
			init = 0;
			now = 1200;
			for (int i = 0;i < S.size();i++) {
				if (S[i] == '0') {
					now--;
				}
				else {
					if (now < 1200) {
						now++;
						init++;
						if (init == A) {
							cout << i + 1;
							return 0;
						}
					}
				}
			}
		}
		ll loop = 0;
		for (int i = 0;i < N;i++)if (S[i] == '1')loop++;
		ll cnt = (A - init - 1) / loop;
		ll ansans = init + cnt * loop;
		now = J;
		for (int i = 0;i < S.size();i++) {
			if (S[i] == '0') {
				now--;
			}
			else {
				if (now < 1200) {
					ansans++;
					now++;
					if (ansans == A) {
						cout << (1LL + cnt) * N + i + 1LL;
						return 0;
					}
				}
			}
		}
	}
	else {
		ll init = 0;
		ll loop = 0;
		int now = 1200;
		for (int i = 0;i < S.size();i++) {
			if (S[i] == '0') {
				now--;
			}
			else {
				if (now < 1200) {
					now++;
					init++;
				}
			}
		}
		if (A <= init) {
			init = 0;
			now = 1200;
			for (int i = 0;i < S.size();i++) {
				if (S[i] == '0') {
					now--;
				}
				else {
					if (now < 1200) {
						now++;
						init++;
						if (init == A) {
							cout << i + 1;
							return 0;
						}
					}
				}
			}
		}
		now = J;
		for (int i = 0;i < S.size();i++) {
			if (S[i] == '0') {
				now--;
			}
			else {
				if (now < 1200) {
					now++;
					loop++;
				}
			}
		}
		ll cnt = (A - init - 1) / loop;
		ll ansans = init + cnt * loop;
		now = J;
		for (int i = 0;i < S.size();i++) {
			if (S[i] == '0') {
				now--;
			}
			else {
				if (now < 1200) {
					ansans++;
					now++;
					if (ansans == A) {
						cout << (1LL + cnt) * N + i + 1LL;
						return 0;
					}
				}
			}
		}
	}
	return 0;
}