//include
//------------------------------------------
#include <bits/stdc++.h>
using namespace std;

//typedef
//------------------------------------------
typedef long long LL;
typedef vector<LL> VL;
typedef vector<VL> VVL;
typedef vector<string> VS;
typedef pair<LL, LL> PLL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);
const int MOD = 1000000007;

// grid
//--------------------------------------------
VL dx = {0, 1, 0, -1};
VL dy = {1, 0, -1, 0};
VL dx2 = {-1, 0, 1, -1, 1, -1, 0, 1};
VL dy2 = {-1, -1, -1, 0, 0, 1, 1, 1};

//debug
//--------------------------------------------
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

//IO accelerate
//--------------------------------------------
struct InitIO {
	InitIO() {
		cin.tie(nullptr);
		ios_base::sync_with_stdio(false);
		cout << fixed << setprecision(30);
	}
} init_io;

//template
//--------------------------------------------
template<typename T>
istream& operator >>(istream& is, vector<T>& vec) {
	for(T& x: vec) is >> x;
	return is;
}
template<typename T>
ostream& operator <<(ostream& os, const vector<T>& vec) {
	for(int i=0; i<vec.size(); i++){
		os << vec[i] << ( i+1 == vec.size() ? "" : "\t" );
	}
	return os;
}
template<typename T>
ostream& operator <<(ostream& s, const vector<vector<T>>& vv) {
	for (int i = 0; i < vv.size(); ++i) {
		s << vv[i] << endl;
	}
	return s;
}

// 多重vector
// auto dp=make_v<int>(4,h,w) みたいに使える
template<typename T>
vector<T> make_v(size_t a){return vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
	return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

// 多重vectorのためのfill
// fill_v(dp,0) みたいに使える
template<typename T,typename V>
typename enable_if<is_class<T>::value==0>::type
fill_v(T &t,const V &v){t=v;}

template<typename T,typename V>
typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t,const V &v){
	for(auto &e:t) fill_v(e,v);
}

//main code

int main(int argc, char *argv[])
{
	LL n,m;
	cin >> n >> m;
	VL a(n);
	cin >> a;
	sort(RALL(a));
	LL const AMAX = 1000000;
	LL ans = 0;
	VL rui(n+1), d(AMAX+1,0);
	rui[0] = 0;
	for (LL i = 0; i < n; ++i) {
		rui[i+1] = rui[i] + a[i];
		d[a[i]]++;
	}
	for (LL i = AMAX; i > 0; i--) {
		d[i-1] += d[i];
	}
	auto isOk = [&](LL mid){
		// M回以下ならtrueとする
		LL numOk = 0;
		for (LL i = 0; i < n; i++) {
			numOk += d[(mid - a[i] < 0 ? 1 : mid - a[i])];
		}
		if (numOk > m) return false;
		else return true;
	};
	// ng:false，ok:true
	LL ng = -1, ok = AMAX+1;
	while (abs(ng - ok) > 1) {
		LL mid = (ok + ng) / 2;
		(isOk(mid) ? ok : ng) = mid;
	}

	LL numOk = 0;
	for (LL i = 0; i < n; i++) {
		LL okv = d[(ok - a[i] < 0 ? 1 : ok - a[i])];
		ans += a[i]*okv + rui[okv];
		numOk += okv;
	}

	ans += ng*(m - numOk);
	cout << ans << endl;
	return 0;
}


Measured memory_bytes: 9600