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

#define nl "\n"
#define ll long long
#define mod  1'000'000'007
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define sz(v) (int) v.size()

template<typename T = int>
istream &operator>>(istream &in, vector<T> &v) {
    for (auto &x: v) in >> x;
    return in;
}

template<typename T = int>
ostream &operator<<(ostream &out, const vector<T> &v) {
    for (const T &x: v) out << x << " ";
    return out;
}

void Sira() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

void solve() {
    int n , k;
    cin >> n >> k;

    map < ll  , int > mp;

    ll entry;
    for (int i = 0; i < n; i++) {
        cin >> entry;
        mp[entry]++;
    }

    if (k == 0) {
        if (mp.begin() -> first == 1) {
            cout << -1 << nl;
        } else {
            cout << 1 << nl;
        }
        return;
    }

    int cnt = 0;

    for (auto &[f , s] : mp) {
        cnt += s;
        if (cnt == k) {
            return void(cout << f << nl);
        }
    }
    cout << -1 << nl;

}

int main() {
    Sira();
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}