#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
const long long LINF = 1e18;
inline long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
template <class S, class T>
ostream& operator<<(ostream& out, const pair<S, T>& o) {
  out << "(" << o.first << "," << o.second << ")";
  return out;
}
template <class T>
ostream& operator<<(ostream& out, const vector<T> V) {
  for (int i = 0; i < V.size(); i++) {
    out << V[i];
    if (i != V.size() - 1) out << " ";
  }
  return out;
}
template <class T>
ostream& operator<<(ostream& out, const vector<vector<T> > Mat) {
  for (int i = 0; i < Mat.size(); i++) {
    if (i != 0) out << endl;
    out << Mat[i];
  }
  return out;
}
template <class S, class T>
ostream& operator<<(ostream& out, const map<S, T> mp) {
  out << "{ ";
  for (auto it = mp.begin(); it != mp.end(); it++) {
    out << it->first << ":" << it->second;
    if (mp.size() - 1 != distance(mp.begin(), it)) out << ", ";
  }
  out << " }";
  return out;
}
template <class Type>
Type solve(Type res = Type()) {
  long long N, K, Q;
  cin >> N >> K >> Q;
  vector<long long> A(N);
  for (auto& in : A) cin >> in;
  sort(A.begin(), A.end());
  res = A[Q - 1] - A[0];
  return res;
}
int main(void) {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(15) << solve<long long>() << endl;
  return 0;
}
