#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];
    int cnt = 0;
    int L = 1, R = n - 1;
    while (L < R) {
        if (L == index) L++;
        else if (R == index) R--;
        else if (a[L] + a[R] <= score) L++;
        else {
            cnt++;
            L++; R--;
        }
    }

    return cnt < m;
}

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

    a[n] = -1;

    int ng = 0;
    int ok = n;
    while(abs(ok - ng) > 1){
        int mid = (ok + ng) / 2;
        if (C(mid)) ok = mid;
        else ng = mid;
    }
    
    cout << a[ok] << endl;

    return 0;
}