use std::io::*;

use std::str::*;
use std::cmp::*;
use std::fmt;
fn main() {
    let n:usize = read();
    let m:i64 = read();
    let mut a:Vec<i32>=vec![0;n-1];
    let k:i32 = read();
    for i in 0..(n-1){
        let b:i32 = read();
        a[i] = b;
    }
    a.sort();
    let mut up:i32 = (n-1) as i32;
    let mut low:i32 = -1;
    let mut flag:bool = false;
    while up - low > 1{
        let mut mid:usize = ((up+low)/2) as usize;
        let val = k + &a[mid];
        let mut s:usize = 0;
        let mut t:usize = n - 2;
        let mut cnt = 0;

        //println!("#######{} {} {}######",mid,a[mid],cnt);
        for i in 0 .. ((n-2)/2){
            if s == mid {
                s += 1;
            }
            if t == mid{
                t -= 1;
            }
         //   println!("{} {} {} {}",s,t,a[s]+a[t],val);
            if a[s] + a[t] > val {
                s += 1;
                t -= 1;
                cnt += 1;
            }else {
                if s + 1 == mid {
                    s += 1;
                }
                s += 2;
            }
        }

        if cnt < m {
            up = mid as i32;
            flag = true;
        } else {
            low = mid as i32;
        }
    }
    println!("{}",(if flag { a[up as usize]}else{-1}));
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let s = stdin.bytes().map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect::<String>();
    s.parse::<T>().unwrap_or_else(|_| panic!("Faild to parse {}", s))
}