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