#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, x, y, i, cnt = 0;
  string s;
  cin >> n >> x >> y;
  cin >> s;
  reverse(s.begin(), s.end());
  i = 0;
  while (i < x) {
    if (i == y && s[i] != '1')
      cnt++;
    else if (i != y && s[i] != '0')
      cnt++;
    i++;
  }
  cout << cnt << "\n";
}
