#include <bits/stdc++.h>

using namespace std;

int n, K;
string s;
int d[55][55];

int main(void) {
  cin >> n >> K >> s;

  fill(d[0], d[55], 1 << 20);
  d[0][0] = 0;
  d[0][1] = 1;
  for (int i = 0; i < n; i++) {
    if (s[i] == '0') {
      d[i + 1][(i + 1) % n + 1] = 1;
    } else if (s[i] == '1') {
      d[i + 1][(i + 1) % n + 1] = 0;
    } else {
      d[i + 1][(i + 1) % n + 1] = 0;
      d[i + 1][(i + 2) % n + 1] = 0;
    }
  }

  for (int k = 0; k <= n; k++) {
    for (int i = 0; i <= n; i++) {
      for (int j = 0; j <= n; j++) {
        d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
      }
    }
  }
  cout << d[0][1] + d[1][1] * ((K - 1) / n) + d[1][(K - 1) % (n - 1) + 1] * ((K - 1) % (n - 1) != 0) << endl;

  return 0;
}