#include <bits/stdc++.h>
const long long INF = 1e9 + 7, mod = 998244353, p = 37;
const long double pi = 3.141592653589793238462, EPS = 1e-10;
using namespace std;
namespace in_out {
template <typename T1, typename T2>
ostream& operator<<(ostream& out, pair<T1, T2> a) {
  out << a.first << " " << a.second;
  return out;
}
template <typename T1, typename T2>
istream& operator>>(istream& in, pair<T1, T2>& a) {
  in >> a.first >> a.second;
  return in;
}
template <typename T>
ostream& operator<<(ostream& out, vector<T> a) {
  for (auto i : a) out << i << " ";
  return out;
}
template <typename T>
istream& operator>>(istream& in, vector<T>& a) {
  for (int i = 0; i < a.size(); i++) in >> a[i];
  return in;
}
}  // namespace in_out
using namespace in_out;
int main() {
  int n, x, y;
  cin >> n >> x >> y;
  string second;
  cin >> second;
  reverse(second.begin(), second.end());
  int ans = 0;
  for (int i = 0; i < x; i++) {
    if (i != y && second[i] == '1') {
      second[i] = '0';
      ans++;
    } else if (i == y && second[i] == '0') {
      second[i] = '1';
      ans++;
    }
  }
  cout << ans;
}
