#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const long long MAX = 5100000;
const long long INF = 1LL << 60;
const long long mod = 1000000007LL;
//const long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;


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

	ll N, K; scanf("%lld %lld", &N, &K);
	string s; cin >> s;
	ll sum = 0;
	ll hako = (K + N - 1) / N;
	if (hako < 5) {
		ll cnt = 0;
		ll res = 0;
		ll rm = 0;
		while (cnt < K) {
			for (ll i = 0; i < N && cnt < K; i++) {
				cnt++;
				if (rm == 0) res++;
				else rm--;
				rm += s[i] - '0';

			}
		}
		cout << res << endl;
	}
	else {
		ll cnt = 0;
		ll res = 0;
		ll rm = 0;
		ll tmp = 0;
		for (ll i = 0; i < N && cnt < K; i++) {
			cnt++;
			if (rm == 0) res++;
			else rm--;
			rm += s[i] - '0';
			tmp += s[i] - '0';

		}
		if (tmp >= N) cout << res << endl;
		else {

			cnt += (hako - 2) * N;
			res += (N - tmp) * (hako - 2);
			for (ll i = 0; i < N && cnt < K; i++) {
				cnt++;
				if (rm == 0) res++;
				else rm--;
				rm += s[i] - '0';

			}
			cout << res << endl;

		}
	}
	return 0;
}