#include <bits/stdc++.h>
using namespace std;
#define FOR(i, n) for(int i = 0; i < (n); i++)
#define MEM(a, x) memset(a, x, sizeof(a))
#define ALL(a) a.begin(), a.end()
#define UNIQUE(a) a.erase(unique(ALL(a)), a.end())
typedef long long ll;
typedef pair<int, int> P;

int n, k;
string s;

int main(int argc, char const *argv[]) {
	ios_base::sync_with_stdio(false);
	cin >> n >> k >> s;
	int cur = 0, ans = 0;
	FOR(i, k) {
		if (cur == 0) {
			ans++;
			cur += s[i%n]-'0';
		}
		else {
			cur--;
			cur += s[i%n]-'0';
		}
	}
	cout << ans << endl;
	return 0;
}