#include <bits/stdc++.h>
#include <time.h>
#include <stdlib.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define pb push_back
#define IOS ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define ll long long
#define ull unsigned long long
#define gcd(a,b) __gcd((a),(b))
#define lcm(a,b) ((a)*(b))/__gcd((a),(b))
#define clr(x) x.clear()
#define vi vector<int>
#define vll vector<long long>
#define vvi vector<vi>
#define mp make_pair
#define hell 1000000007
#define pii pair<int,int>
#define pll pair<ll,ll>
#define vpii vector<pii>
#define vpll vector<pll>
#define all(a) a.begin(),a.end()
#define ign cin.ignore();

#define o_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define o_setll tree<ll, null_type,less<ll>, rb_tree_tag,tree_order_statistics_node_update>
//member functions :
//1. order_of_key(k) : number of elements strictly lesser than k
//2. find_by_order(k) : k-th element in the set

using namespace std;
using namespace __gnu_pbds;

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

using cd = complex<double>;
const double PI = acos(-1);

void fft(vector<cd> & a, bool invert) {
    ll n = a.size();

    for (ll i = 1, j = 0; i < n; i++) {
        ll bit = n >> 1;
        for (; j & bit; bit >>= 1)
            j ^= bit;
        j ^= bit;

        if (i < j)
            swap(a[i], a[j]);
    }

    for (ll len = 2; len <= n; len <<= 1) {
        double ang = 2 * PI / len * (invert ? -1 : 1);
        cd wlen(cos(ang), sin(ang));
        for (ll i = 0; i < n; i += len) {
            cd w(1);
            for (ll j = 0; j < len / 2; j++) {
                cd u = a[i+j], v = a[i+j+len/2] * w;
                a[i+j] = u + v;
                a[i+j+len/2] = u - v;
                w *= wlen;
            }
        }
    }

    if (invert) {
        for (cd & x : a)
            x /= n;
    }
}

vector<ll> multiply(vector<ll> const& a, vector<ll> const& b) {
    vector<cd> fa(a.begin(), a.end()), fb(b.begin(), b.end());
    ll n = 1;
    while (n < a.size() + b.size())
        n <<= 1;
    fa.resize(n);
    fb.resize(n);

    fft(fa, false);
    fft(fb, false);
    for (ll i = 0; i < n; i++)
        fa[i] *= fb[i];
    fft(fa, true);

    vector<ll> result(n);
    for (ll i = 0; i < n; i++)
        result[i] = round(fa[i].real());
    return result;
}

vll a,res;

#define MAXI 100010

int main()
{
    IOS
    a.resize(MAXI);
    ll n,m;
    cin>>n>>m;
    int temp;
	for (int i = 0; i < n; i++){
		cin>>temp;
		a[temp]++;
	}
	res = multiply(a, a);
    ll val=(ll)res.size()-1;
    ll print=0;
    while(m){
        ll pres=res[val];
        ll mini=min(pres,m);
        print=print+mini*val;
        val--;
        m-=mini;
    }
    cout<<print;
    return 0;
}


Measured memory_bytes: 11464