#include <bits/stdc++.h>   using namespace std;   long long GCD(long long u, long long v) {     long long r;     while (v) {       r = u % v;       u = v;       v = r;     }     return u;   }   long long modpow(long long a, long long p, long long mod) {     long long ret = 1;     while (p) {       if (p & 1) ret = (ret * a) % mod;       a = (a * a) % mod;       p /= 2;     }     return ret;   }   long long power(long long a, long long p) {     long long ret = 1;     while (p) {       if (p & 1) ret = (ret * a);       a = (a * a);       p /= 2;     }     return ret;   }   int a[51];   int main() {     int i, j, tmp;     ios_base::sync_with_stdio(0);     cin.tie(NULL);     int n, k;     cin >> n >> k;     for (i = 0; i < n; i++) cin >> a[i];     sort(a, a + n);     if (k > n)       cout << -1 << endl;     else       cout << a[n - k] <<     << a[n - k] << endl;     return 0;   }   