#![allow(unused_imports, unused_macros, dead_code)]

macro_rules! min {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        it.next().map(|z| it.fold(z, |x, y| min!(x, y)))
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = min!($($ys),*);
        if $x < t { $x } else { t }
    }}
}
macro_rules! max {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        it.next().map(|z| it.fold(z, |x, y| max!(x, y)))
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = max!($($ys),*);
        if $x > t { $x } else { t }
    }}
}

macro_rules! ewriteln {
    ($($args:expr),*) => { let _ = writeln!(&mut std::io::stderr(), $($args),*); };
}
macro_rules! trace {
    ($x:expr) => { ewriteln!(">>> {} = {:?}", stringify!($x), $x) };
    ($($xs:expr),*) => { trace!(($($xs),*)) }
}
macro_rules! put {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        if let Some(x) = it.next() { print!("{}", x); }
        for x in it { print!(" {}", x); }
        println!("");
    }};
    ($x:expr) => { println!("{}", $x) };
    ($x:expr, $($xs:expr),*) => { print!("{} ", $x); put!($($xs),*) }
}

const M: i64 = 1_000_000_007;

fn bsearch(xs: &Vec<u64>, x: u64) -> usize {
    if xs[0] >= x { return 0 }
    let mut left = 0;  // xs[left] < x
    let mut right = xs.len();  // xs[right] >= x
    while left + 2 <= right {
        let mid = (left + right) / 2;
        if xs[mid] < x {
            left = mid;
        } else {
            right = mid;
        }
    }
    right
}

fn handshakes(xs: &Vec<u64>, z: u64, acc: &Vec<u64>) -> (usize, u64) {
    // z 以上の握手の個数とその和
    let n = xs.len();
    let mut count = 0;
    let mut sum = 0;
    for &x in xs.iter() {
        let comp = if z > x { z - x } else { 0 };
        let i = bsearch(&xs, comp);
        let c = xs.len() - i;
        count += c;
        sum += (acc[n] - acc[i]) + (x * c as u64);
    }
    (count, sum)
}

fn main() {
    let mut sc = Scanner::new();
    let n: usize = sc.cin();
    let m: usize = sc.cin();
    let mut xs: Vec<u64> = sc.vec(n);
    xs.sort();

    let mut acc: Vec<u64> = vec![0; n + 1];
    for i in 0..n {
        acc[i + 1] = acc[i] + xs[i];
    }

    let mut left: u64 = 0;  // Count(>= left) > m
    let mut right: u64 = xs[n - 1] * 2 + 10000; // Count(>= right) <= m

    for _ in 0..20 {
        let mid = (left + right) / 2;
        if handshakes(&xs, mid, &acc).0 > m {
            left = mid;
        } else {
            right = mid;
        }
    }

    let (count, sum) = handshakes(&xs, right, &acc);
    let ans = sum + (m - count) as u64 * (right - 1);
    put!(ans);
}

use std::io::{self, Write};
use std::str::FromStr;
use std::collections::VecDeque;

struct Scanner { stdin: io::Stdin, buffer: VecDeque<String>, }
impl Scanner {
    fn new() -> Self { Scanner { stdin: io::stdin(), buffer: VecDeque::new() } }
    fn cin<T: FromStr>(&mut self) -> T {
        while self.buffer.len() == 0 {
            let mut line = String::new();
            let _ = self.stdin.read_line(&mut line);
            for w in line.split_whitespace() {
                self.buffer.push_back(String::from(w));
            }
        }
        self.buffer.pop_front().unwrap().parse::<T>().ok().unwrap()
    }
    fn chars(&mut self) -> Vec<char> { self.cin::<String>().chars().collect() }
    fn vec<T: FromStr>(&mut self, n: usize) -> Vec<T> { (0..n).map(|_| self.cin()).collect() }
}


Measured memory_bytes: 11636