#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9, MOD = 1e9 + 7, ohara = 1e6;
const long long LINF = 1e18;
long long int n, cnt = 0, ans = 0, a[ohara], b, c, d, cmp, cmpp, m, h, w, x, y,
                 sum = 0, pos, k, q;
int dy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1};
string alph("abcdefghijklmnopqrstuvwxyz"), s;
bool fl;
struct edge {
  int to, cost;
};
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> k >> q;
  long long mi = LINF;
  for (long long int(i) = 0; (i) < (int)(n); (i)++) {
    cin >> a[i];
    if (mi < a[i]) mi = a[i];
  }
  sort(a, a + n);
  cout << (a[q - 1] - a[0]) << endl;
  return 0;
}
