#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
bool cmin(A &a, const B &b) {
  return a > b ? (a = b, true) : false;
}
template <typename A, typename B>
bool cmax(A &a, const B &b) {
  return a < b ? (a = b, true) : false;
}
const double PI = acos(-1);
const double EPS = 1e-9;
long long inf = sizeof(long long) == sizeof(long long) ? 2e18 : 1e9 + 10;
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};
int main() {
  int n, m, k;
  cin >> n >> m >> k;
  vector<long long> in(n);
  for (int i = 0; i < n; i++) cin >> in[i];
  sort(in.begin(), in.end());
  cout << in[k - 1] - in[0] << endl;
}
