using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using static System.Math;
using static System.Array;
using static AtCoder.Tool;
namespace AtCoder
{
    class AC
    {
        const int MOD = 1000000007;
        const int INF = int.MaxValue / 2;
        const long SINF = long.MaxValue / 2;
        const double EPS = 1e-8;
        static readonly int[] dx = { 0, 1, 0, -1 };
        static readonly int[] dy = { 1, 0, -1, 0 };
        //static List<List<int>> G = new List<List<int>>();
        //static List<List<Edge>>G = new List<List<Edge>>();
        //static List<Edge> E = new List<Edge>();

        static void Main(string[] args)
        {
            //var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            //Console.SetOut(sw);
            var cin = new Scanner();


            var input = cin.ReadSplitLong();
            int N = (int)input[0];
            long M = input[1];
            var A = cin.ReadSplitLong();
            Sort(A);Reverse(A);

            long l = -1;
            long r = 2 * A.Max() + 1;

            long bd = -1;

            //Console.WriteLine(string.Join(",", A));
            while (r - l > 1)
            {
                long mid = (l + r) / 2;
                long cntmax = 0;
                for(var i = 0; i < N; i++)
                {
                    int ll = -1;
                    int rr = N;
                    while (rr - ll > 1)//個数のmax
                    {
                        int mmid = (ll + rr) / 2;
                        if (mid <= A[i] + A[mmid]) { ll = mmid; }
                        else { rr = mmid; }
                    }
                    cntmax += ll + 1;
                }
                //Console.WriteLine($"{mid} {cntmin} {cntmax}");
                if (cntmax >= M) { l = mid; }
                else{ r = mid; }
            }
            bd = l;
            //Console.WriteLine($"bd={bd}");
            long ans = 0;
            long res = M;
            for(var i = 0; i < N; i++)
            {
                l = -1;
                r = N;
                while (r - l > 1)
                {
                    long mid = (l + r) / 2;
                    if (A[i] + A[mid] > bd) { l = mid; }
                    else { r = mid; }
                }
                //Console.WriteLine($"A[{i}]:{l}");
                res -= l + 1;
                ans += 2 * (l + 1) * A[i];
            }
            ans += res * bd;
            Console.WriteLine(ans);
            
            

            //Console.Out.Flush();
        }
        
        struct Edge
        {
            public int from;

            public int to;
            public long dist;
            public Edge(int t, long c)
            {
                from = -1;
                to = t;
                dist = c;
            }
            public Edge(int f, int t, long c)
            {
                from = f;
                to = t;
                dist = c;
            }

        }
    }
    
    public class Scanner
    {
        public int[] ReadSplitInt()
        {
            return ConvertAll(Console.ReadLine().Split(), int.Parse);
        }
        public long[] ReadSplitLong()
        {
            return ConvertAll(Console.ReadLine().Split(), long.Parse);
        }
        public double[] ReadSplit_Double()
        {
            return ConvertAll(Console.ReadLine().Split(), double.Parse);
        }
    }
    public static class Tool
    {
        static public void Initialize<T>(ref T[] array, T initialvalue)
        {
            for (var i = 0; i < array.Length; i++)
            {
                array[i] = initialvalue;
            }
        }
        static public void Swap<T>(ref T a, ref T b)
        {
            T keep = a;
            a = b;
            b = keep;
        }

        static public void Display<T>(T[,] array2d, int n, int m)
        {
            for (var i = 0; i < n; i++)
            {
                for (var j = 0; j < m; j++)
                {
                    Console.Write($"{array2d[i, j]} ");
                }
                Console.WriteLine();
            }
        }

        static public long LPow(int a, int b)
        {
            return (long)Pow(a, b);
        }
    }
}


Measured memory_bytes: 19808