#include <bits/stdc++.h>
using namespace std;
static const int INF = INT_MAX;
static const long long LINF = LLONG_MAX;
static const int MIN = INT_MIN;
static const long long LMIN = LLONG_MIN;
static const int MOD = 1e9 + 7;
static const int SIZE = 200005;
const int dx[] = {0, -1, 1, 0};
const int dy[] = {-1, 0, 0, 1};
vector<long long> Div(long long n) {
  vector<long long> ret;
  for (long long i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n) ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end());
  return ret;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k, q;
  cin >> n >> k >> q;
  vector<long long> v(n);
  for (int i = 0; i < n; ++i) {
    cin >> v[i];
  }
  sort(v.begin(), v.end());
  cout << v[q - 1] - v[0] << endl;
  return 0;
}
