#include <bits/stdc++.h>
using namespace std;
char brr[1000000];
char arr[1000000];
int main() {
  int i, j = 1, k, n, m = 0, x, y;
  char z;
  cin >> n >> x >> y;
  for (i = 0; i <= x; i++) {
    brr[i] = '0';
  }
  brr[0] = '1';
  brr[x - y] = '1';
  for (i = 0; i < n; i++) {
    cin >> z;
    arr[i] = z;
    if (i >= n - x) {
      if (arr[i] != brr[j]) m++;
      j++;
    }
  }
  cout << m << endl;
  return 0;
}
