#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MOD = 1000000007;
const int MAX_N = 100010;

#define REP(i,n) for((i)=0;(i)<(int)(n);(i)++)

int n, m;
int a[MAX_N];

bool C(int index){
    int score = a[0] + a[index];
    priority_queue<int> que;
    for (int i = 1; i < n; i++){
        if (i != index) que.push(a[i]);
    }
    
    for (int i = 1; i <= m; i++){
        ll sum = que.top(); que.pop();
        sum += que.top(); que.pop();
        if (sum <= score) return true;
    }

    return false;
}

int main(){
    cin >> n >> m;
    for (int i = 0; i < n; i++) cin >> a[i];
    sort(a + 1, a + n);

    int ng = -1;
    int ok = n;
    while(abs(ok - ng) > 1){
        int mid = (ok + ng) / 2;
        if (C(mid)) ok = mid;
        else ng = mid;
    }

    if (ok == n){
        cout << -1 << endl;
    }else{
        cout << a[ok] << endl;
    }

    return 0;
}