#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, x, y, cnt = 0;
  cin >> n >> x >> y;
  string s;
  cin >> s;
  n = s.size();
  int p = n - 1 - y;
  for (int i = n - 1; i >= n - x; i--) {
    if (i == p) {
      if (s[i] == '0') {
        s[i] = '1';
        cnt++;
      }
    } else {
      if (s[i] == '1') {
        s[i] = '0';
        cnt++;
      }
    }
  }
  cout << cnt << endl;
}
