#[allow(unused_imports)]
use std::char::from_digit;
#[allow(unused_imports)]
use std::cmp::{max, min};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::fs::File;
#[allow(unused_imports)]
use std::io::prelude::*;
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufReader, BufWriter, Stdin, Stdout, Write};
#[allow(unused_imports)]
use std::mem::swap;
#[allow(unused_imports)]
use std::str::FromStr;

type BoxResult<T> = Result<T, Box<std::error::Error>>;

const L: i64 = 100000;

fn main() {
    let mut scanner = Scanner::new(stdin());
    let (n, m) = scanner.read_two::<usize>().unwrap();
    let mut arr = scanner.read_vector::<i64>().unwrap();
    arr.sort();
    let ans = solve(n, m, &arr);
    println!("{}", ans);
}

fn solve(n: usize, m: usize, arr: &[i64]) -> i64 {
    let lb = calc_lower_bound(m, arr);
    let cumsum = arr.iter().scan(0, |state, val| { 
        *state += *val;
        Some(*state)
    }).collect::<Vec<_>>();
    let mut sum = 0;
    for i in 0..n {
        let index = binary_search(lb - arr[i], arr);
        if index == 0 {
            sum += arr[i] * n as i64 + cumsum[n - 1];
        } else {
            sum += arr[i] * (n - index) as i64 + cumsum[n - 1] - cumsum[index - 1];
        }
    }
    sum -= (count(lb, arr) - m) as i64 * lb;
    sum
}

fn calc_lower_bound(m: usize, arr: &[i64]) -> i64 {
    let (mut l, mut r) = (1, 2 * L);
    if count(r, arr) >= m {
        return r;
    }
    while r - l > 1 {
        let mid = (l + r) / 2;
        if count(mid, arr) >= m {
            l = mid;
        } else {
            r = mid;
        }
    }
    l
}

fn count(x: i64, arr: &[i64]) -> usize {
    let n = arr.len();
    let mut sum = 0;
    for i in 0..arr.len() {
        sum += n - binary_search(x - arr[i], arr);
    }
    sum
}

fn binary_search(x: i64, arr: &[i64]) -> usize {
    if arr[0] >= x {
        return 0;
    }
    if arr[arr.len() - 1] < x {
        return arr.len();
    }
    let (mut l, mut r) = (0, arr.len() - 1);
    while r - l > 1 {
        let mid = (l + r) / 2;
        if arr[mid] < x {
            l = mid;
        } else {
            r = mid;
        }
    }
    r
}

#[allow(dead_code)]
struct Scanner<R> {
    reader: BufReader<R>,
    buffer: String,
}
impl<R> Scanner<R>
where
    R: Read,
{
    #[allow(dead_code)]
    fn new(inner: R) -> Scanner<R> {
        let reader = BufReader::new(inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    #[allow(dead_code)]
    fn with_capacity(capacity: usize, inner: R) -> Scanner<R> {
        let reader = BufReader::with_capacity(capacity, inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    #[allow(dead_code)]
    fn read_line(&mut self) -> BoxResult<String> {
        self.reader.read_line(&mut self.buffer)?;
        let cloned = self.buffer.trim().to_string();
        self.buffer.clear();
        Ok(cloned)
    }
    #[allow(dead_code)]
    fn read<T>(&mut self) -> BoxResult<T>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed = self.buffer.trim().parse()?;
        self.buffer.clear();
        Ok(parsed)
    }
    #[allow(dead_code)]
    fn read_two<T>(&mut self) -> BoxResult<(T, T)>
    where
        T: FromStr,
        T: Copy,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static, 
    {
        let nums = self.read_vector()?;
        Ok((nums[0], nums[1]))
    }
    #[allow(dead_code)]
    fn read_three<T>(&mut self) -> BoxResult<(T, T, T)>
    where
        T: FromStr,
        T: Copy,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static, 
    {
        let nums = self.read_vector()?;
        Ok((nums[0], nums[1], nums[2]))
    }
    #[allow(dead_code)]
    fn read_vector<T>(&mut self) -> BoxResult<Vec<T>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed_vec = self
            .buffer
            .trim()
            .split_whitespace()
            .map(|s| s.parse())
            .collect::<Result<Vec<_>, _>>()?;
        self.buffer.clear();
        Ok(parsed_vec)
    }
    #[allow(dead_code)]
    fn read_matrix<T>(&mut self, lines: usize) -> BoxResult<Vec<Vec<T>>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        let mut parsed_matrix = vec![];
        for _ in 0..lines {
            self.reader.read_line(&mut self.buffer)?;
            parsed_matrix.push(
                self.buffer
                    .trim()
                    .split_whitespace()
                    .map(|s| s.parse())
                    .collect::<Result<Vec<_>, _>>()?,
            );
            self.buffer.clear();
        }
        Ok(parsed_matrix)
    }
    #[allow(dead_code)]
    fn read_chars(&mut self) -> BoxResult<Vec<char>> {
        self.reader.read_line(&mut self.buffer)?;
        let chars = self.buffer.trim().chars().collect::<Vec<_>>();
        self.buffer.clear();
        Ok(chars)
    }
}


Measured memory_bytes: 8444