#include <bits/stdc++.h>
using namespace std;
long long M = 1000000007;
int main() {
  int n, x, y;
  cin >> n >> x >> y;
  string s;
  cin >> s;
  int ans = 0;
  for (int i = 0; i < x; i++) {
    int pos = n - i - 1;
    char current = '0';
    if (i == y) {
      current = '1';
    }
    if (current != s[pos]) {
      ans++;
    }
  }
  cout << ans << '\n';
  return 0;
}
