Less or Equal

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back

signed main()
{
    int n , k;
    cin >> n >> k;
    vector<int> a(n);
    for(int i = 0; i < n; i++)
        cin >> a[i];

    sort(a.begin() , a.end());

    if(k == n){
        cout << (int)1e9 << endl;
        return 0;
    }
    if(!k){
        cout << ((a[0] == 1) ? "-1" : "1") << endl;
        return 0;
    }
    if(a[k - 1] == a[k]){
        cout << "-1" << endl;
        return 0;
    }
    cout << a[k - 1] << endl;
}