#include <bits/stdc++.h>
using namespace std;
long long modx(long long Base, long long exponent) {
  long long ans = 1;
  if (Base == 1) return Base;
  while (exponent) {
    if (exponent & 1) ans = (ans * Base) % 1000000007LL;
    Base = (Base * Base) % 1000000007LL;
    exponent = exponent >> 1;
  }
  return ans;
}
long long inmodx(long long num) { return (modx(num, 1000000007LL - 2LL)); }
bool cmp(pair<long long, long long> a, pair<long long, long long> b) {
  return ((a.second * b.first) <= (b.second * a.first));
}
const int N = (2e5) + 9;
const int M = (N << 2) + 9;
const int LOGN = ((int)log2(N)) + 3;
const int LOGM = ((int)log2(M)) + 3;
const int BUCK = 650;
int a[N];
void solve() {
  int n, k, q, i, ans;
  cin >> n >> k >> q;
  for (i = (1); i < (n + 1); i++) cin >> a[i];
  sort(a + 1, a + n + 1);
  ans = a[q] - a[1];
  cout << ans << '\n';
  return;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t = 1, cs;
  for (cs = (1); cs < (t + 1); cs++) {
    solve();
  }
  return 0;
}
