#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;

using isize = size_t;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;
using f64 = long double;
using p2 = pair<i64, i64>;
using el = tuple<i64, i64, i64>;
using mint = atcoder::modint998244353;

void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(18);
  _main();
}

i64 pow(i64 x, i64 n) {
  i64 res = 1;
  i64 t = x;
  while (n > 0) {
    if (n & 1) res *= t;
    t *= t;
    n >>= 1;
  }
  return res;
}

void _main() {
  i64 n, a;
  cin >> n >> a;
  a--;
  string s;
  cin >> s;
  vector<i64> u, v;
  i64 now = 0;
  for (i64 i = 0; i < n; i++) {
    if (s[i] == '0') now--;
    else if (now < 0) now++, u.push_back(i);
  }
  for (i64 i = 0; i < n; i++) {
    if (s[i] == '0') now--;
    else if (now < 0) now++, v.push_back(i);
  }
  if (a < u.size()) {
    cout << u[a] + 1 << "\n";
    return;
  }
  a -= u.size();
  i64 x = a / v.size() + 1;
  i64 y = a % v.size();
  cout << x * n + v[y] + 1 << "\n";
}