#include <bits/stdc++.h>
using namespace std;
const long long INF =
    sizeof(long long) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const long long MOD = (long long)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  long long N, K, Q;
  cin >> N >> K >> Q;
  vector<long long> v(N);
  for (long long i = (0); i < (N); i++) {
    cin >> v[i];
  }
  sort(begin(v), end(v));
  cout << (v[Q - 1] - v[0]) << endl;
  return 0;
}
