#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, x, y;
  cin >> n >> x >> y;
  string s;
  cin >> s;
  string s1 = "1";
  while (x--) {
    if (x == y) {
      s1 += '1';
    } else {
      s1 += '0';
    }
  }
  int j = s.size() - 1;
  int cnt = 0;
  for (int i = s1.size() - 1; i > 0; i--) {
    if (s1[i] != s[j]) {
      cnt++;
    }
    j--;
  }
  cout << cnt << endl;
  return 0;
}
