#include <bits/stdc++.h>   using namespace std;   int main() {     long long int n, a, b, diff;     cin >> n >> a >> b;     vector<long long int> v;     long long int arr[n];     for (long long int i = 0; i < n; i++) {       cin >> arr[i];       v.push_back(arr[i]);     }     sort(v.begin(), v.end());     diff = v[n - a] - v[b - 1];     if (diff < 0) {       cout <<  0  << endl;     } else {       cout << diff << endl;     }   }   