#include <bits/stdc++.h>
#define ll long long

using namespace std;

int main() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    int n, k;
    cin >> n >> k;
    map<int,int>m; //freq
    while (n--) {
        int x; cin >> x;
        m[x]++;
    }
    ll ans=0;
    for (auto [i,v] :m) {
        ans+=v;
        if (ans==k) {
            cout << i << endl;
            return 0;
        }
        if (ans>k) {
            cout << -1 << endl;
            return 0;
        }
    }
    if (ans==k) cout << 1000000000 << endl;
    else cout << -1 << endl;
    return 0;
}

/*
 *
 *
 */