#include <bits/stdc++.h>
using namespace std;
bool Check(int N, int pos) { return (bool)(N & (1 << pos)); }
int Set(int N, int pos) { return N = N | (1 << pos); }
int fx[] = {+0, +0, +1, -1, -1, +1, -1, +1};
int fy[] = {-1, +1, +0, +0, +1, +1, -1, -1};
int hr[] = {-2, -2, -1, +1, +2, +2, -1, +1};
int hc[] = {+1, -1, +2, +2, -1, +1, -2, -2};
int dx[] = {+1, -1, +0, +0};
int dy[] = {+0, +0, +1, -1};
const int MAXN = (int)1e5 + 9;
int main() {
  int i, j, k, l, m, n, p, q, x, y, u, v, r, tc, t;
  string s;
  cin >> n >> x >> y;
  cin >> s;
  string ss = "";
  for (i = n - 1, j = 0; j < x; i--, j++) ss += s[i];
  reverse(ss.begin(), ss.end());
  string rem = "1";
  for (i = 0; i < y; i++) rem += "0";
  int cnt = 0;
  for (i = ss.size() - 1, j = rem.size() - 1; j >= 0; i--, j--) {
    if (ss[i] == rem[j])
      continue;
    else
      cnt++;
  }
  for (; i >= 0; i--) {
    if (ss[i] == '1') cnt++;
  }
  cout << cnt << endl;
  return 0;
}
