#include <bits/stdc++.h>
using namespace std;
template <class T>
inline T bigMod(T p, T e, T M) {
  long long ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p) % M;
    p = (p * p) % M;
  }
  return (T)ret;
}
template <class T>
inline T modInverse(T a, T M) {
  return bigMod(a, M - 2, M);
}
template <class T>
inline T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
template <class T>
inline T lcm(T a, T b) {
  a = abs(a);
  b = abs(b);
  return (a / gcd(a, b)) * b;
}
template <class T>
inline T diss(T x1, T x2, T y1, T y2) {
  return sqrt(((x1 - x2) * (x1 - x2)) + ((y1 - y2) * (y1 - y2)));
}
template <class T>
inline string int2String(T a) {
  ostringstream str;
  str << a;
  return str.str();
}
template <class T>
inline T string2int(string a) {
  stringstream str(a);
  T b;
  str >> b;
  return b;
}
const int dr[] = {0, 1, 0, -1, -1, 1, 1, -1, -2, -2, 2, 2, -1, -1, 1, 1};
const int dc[] = {1, 0, -1, 0, 1, 1, -1, -1, -1, 1, -1, 1, -2, 2, -2, 2};
bool sortbysec(const pair<long long, long long> &a,
               const pair<long long, long long> &b) {
  return (a.second < b.second);
}
long long floorSqrt(long long x) {
  if (x == 0 || x == 1) return x;
  long long start = 1, end = x, ans;
  while (start <= end) {
    long long mid = (start + end) / 2;
    if (mid * mid == x) return mid;
    if (mid * mid < x) {
      start = mid + 1;
      ans = mid;
    } else
      end = mid - 1;
  }
  return ans;
}
bool is_prime(long long n) {
  if (n == 1) return false;
  long long anp = sqrt(n);
  for (long long i = 2; i <= anp; i++)
    if (n % i == 0) return false;
  return true;
}
long long factorials(int n) {
  if (!n) return 1;
  return n * factorials(n - 1);
}
long long dig_sum(long long x) {
  long long sm = 0;
  while (x) {
    sm += (x % 10);
    x /= 10;
  }
  return sm;
}
int main() {
  long long n, x, y;
  scanf("%lld %lld %lld", &n, &x, &y);
  string s;
  cin >> s;
  int ans = 0;
  if (s[n - y - 1] == '1')
    ans--;
  else if (s[n - y - 1] == '0')
    ans++;
  for (int i = n - 1, j = 0; j < x; i--, j++) {
    if (s[i] == '1') ans++;
  }
  cout << ans << endl;
  return 0;
}
