#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
int n, x, y, t;
string s;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  t = 1;
  while (t--) {
    cin >> n >> x >> y;
    cin >> s;
    reverse(s.begin(), s.end());
    int res = 0;
    for (int i = 0; i < x; ++i) {
      if (s[i] == '1') {
        ++res;
      }
    }
    if (s[y] == '1') {
      --res;
    } else {
      ++res;
    }
    cout << res << endl;
  }
  return 0;
}
