#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
typedef long long int ll;
const int N = 100000;
ll pt[N - 1], a, n, m,mi=n-1,mn=-1;

bool cg(int si) {
	int mi1 = n - 2 - 2 * (m - 1),mi2=mi1-1;
	if (mi1 <= si)mi1--;
	if (mi2 <= si)mi2--;
	return pt[mi1] + pt[mi2] <= a + pt[si];
}

int main() {
	cin >> n >> m;
	cin >> a;
	for (int i = 0; i < n - 1; i++)cin >> pt[i];
	sort(pt, pt + n - 1);
	for (int i = 0; i < n - 1; i++)if (cg(i)) { cout << pt[i] << endl; goto end; }
	cout << -1 << endl;
	end:return 0;
}