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