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