#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iterator>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <utility>
#include <memory>
#include <functional>
#include <deque>
#include <cctype>
#include <ctime>
#include <numeric>
#include <list>
#include <iomanip>

#if __cplusplus >= 201103L
#include <array>
#include <tuple>
#include <initializer_list>
#include <forward_list>

#define cauto const auto&
#else

#endif

using namespace std;


typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll;
typedef vector<vector<long long> > vvll;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}

#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define _rep(i,n) _rep2((i),0,(n))
#define _rep2(i,a,b) for(int i=(a);i<(b);++i)
#define rep(...) GET_MACRO(__VA_ARGS__, _rep2, _rep)(__VA_ARGS__)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define fi first
#define se second
#define mkp make_pair
#define DEBUG
#ifdef DEBUG
#define dump(x)  cout << #x << " = " << (x) << endl;
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#else
#define dump(x)
#define debug(x)
#endif

#define MOD 1000000007LL
#define EPS 1e-8
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
#define maxs(x,y) x=max(x,y)
#define mins(x,y) x=min(x,y)

bool check(ll mid, vint &A, ll M) {
    int idx = A.size()-1;
    ll cnt = 0;
    rep(i, A.size()) {
        while(idx>=i && A[idx]+A[i]<mid) {
            idx--;
        }
        if (idx < i) {
            return cnt >= M;
        }
        cnt += (idx - i)*2 + 1;
    }
    return cnt >= M;
}

ll calc(ll x, vint &A, ll M) {
    int idx = A.size()-1;
    ll cnt = 0;
    ll ans = 0;
    ll sum = 0;
    rep(i, A.size()) {
        sum += A[i];
    }

    rep(i, A.size()) {
        while(idx>=i && A[idx]+A[i]<x) {
            sum -= A[idx--];
        }
        if (idx < i) {
            break;
        }
        cnt += (idx - i)*2 + 1;
        ans += A[i]*2;
        sum -= A[i];
        ans += sum*2 + 2LL*A[i]*(idx-i);
    }
    return ans + (M - cnt)*(x-1);
}

void mainmain(){
    int N;
    ll M;
    cin >> N >> M;
    vint A(N);
    rep(i, N) cin >> A[i];
    sort(ALL(A));
    reverse(ALL(A));

    ll l = 0;
    ll r = INFL;

    while (r-l>1) {
        ll mid = (r+l)/2;
        if (check(mid, A, M)) {
            l = mid;
        }
        else {
            r = mid;
        }
    }

//    cout << r << endl;

    cout << calc(r, A, M) << endl;
}


signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout<<fixed<<setprecision(20);
    mainmain();
}

Measured memory_bytes: 640