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