#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define pli pair<ll, int>
#define pil pair<int, ll>
#define pll pair<ll, ll>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\n'
const int inf = 1000000007;
const ll INF = 1e18;
// int mod = 998244353;
int mod = 1000000007;
const double eps = 1e-8;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { if (a > b) { a = b; return 1; } return 0; }
template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { if (a < b) { a = b; return 1; } return 0; }
ll gcd(ll a, ll b) { if (b == 0) return a; return gcd(b, a % b); }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template<typename T, typename U> T pow_(T a, U b) { return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1; }
ll modpow(ll a, ll b, ll _mod) { return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1; }
template<class T, class U> ostream& operator << (ostream& os, const pair<T, U>& p) { os << p.F << " " << p.S; return os; }
template<class T> ostream& operator << (ostream& os, const vector<T>& vec) { rep(i, sz(vec)) { if (i) os << " "; os << vec[i]; } return os; }
template<class T> ostream& operator << (ostream& os, const set<T>& s) { for (auto si : s) os << si << " "; return os; }
template<typename T> inline istream& operator >> (istream& is, vector<T>& v) { rep(j, sz(v)) is >> v[j]; return is; }
template<class T, class T2> inline void add(T &a, T2 b) { a += b % mod; if (a >= mod) a -= mod; }
template<class T> void operator += (vector<T>& v, vector<T> v2) { rep(i, sz(v2)) v.eb(v2[i]); }

void solve();

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cout << fixed << setprecision(12); // debuged
    int T;
    T = 1;
    while (T--) solve();
}

// https://atcoder.jp/contests/abc149/submissions/16070825
// debuged, long long
void solve() {
    int n; ll m;
    cin >> n >> m;
    vector<int> a(n);
    cin >> a;
    sort(all(a));
    
    auto bin = [&](int ok, int ng) {
        auto check = [&](int x) {
            ll cnt = 0;
            rep(i, n) {
                int j = lb(a, x - a[i]);
                if (j == n) continue;
                cnt += n - j;
            }
            if (cnt >= m) return 1;
            return 0;
        };
        while (abs(ok - ng) > 1) {
            int mid = (ok + ng) / 2;
            if (check(mid)) ok = mid;
            else ng = mid;
        }
        return ok;
    };
    int x = bin(0, 2 * 100000 + 1); // この幸福度以上の握手がm回以上できるか
    
    // cnt>mの境界では最小値がcnt-m個ある
    vector<ll> acc(n + 1);
    rep(i, n) acc[i + 1] = acc[i] + a[i];
    
    int mi = inf;
    ll cnt = 0, sum = 0;
    rep(i, n) {
        int j = lb(a, x - a[i]);
        if (j == n) continue;
        cnt += n - j;
        sum += (n - j) * 1LL * a[i] + (acc[n] - acc[j]);
        chmin(mi, a[i] + a[j]);
    }
    cout << sum - (cnt - m) * 1LL * mi << endl;
}



Measured memory_bytes: 4528