#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k, q;
  cin >> n >> k >> q;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  cout << a[q - 1] - a[0] << endl;
}
