#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i< (n); ++i)
#define repi(i, a, b) for (int i = (a); i < (b); ++i)
#define all(x) (x).begin(), (x).end()
#define fore(i, a) for(auto &i:a)
using ll = long long;
#define DEBUG(x) cerr << #x << ": "; for (auto _ : x) cerr << _ << " "; cerr << endl;
int main() {
	ll n,a; cin >> n >> a;
	string s;cin >> s;
	ll now = 1200;
	ll ac1 = 0;
	ll ac2 = 0;
	vector<ll> ivent1, ivent2;
	rep(i, n){
		if(s[i] == '1' && now < 1200){
			ac1++;
			ivent1.push_back(i);
			now++;
		}
		else if(s[i] == '0'){
			now--;
		}
	}
	rep(i, n){
		if(s[i] == '1' && now < 1200){
			ac2++;
			ivent2.push_back(i);
			now++;
		}
		else if(s[i] == '0'){
			now--;
		}
	}
	int ans;
	if(a <= ac1){
		ans = ivent1[a-1]+1;
	}
	else{
		a -= ac1;
		auto[q, r] = div(a, ac2);
		if(r == 0){
			ans = q*n+ivent2[ac2-1];
		}
		else{
			ans = (q+1)*n+ivent2[r-1]+1;
		}
	}
	cout << ans << endl;
		

}