#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
using Graph = vector<VecP>;
template <typename T>
using Vec1 = vector<T>;
template <typename T>
using Vec2 = vector<Vec1<T> >;
#define REP(i, m, n) for(ll i = (m); i < (n); ++i)
#define REPN(i, m, n) for(ll i = (m); i <= (n); ++i)
#define REPR(i, m, n) for(ll i = (m)-1; i >= (n); --i)
#define REPNR(i, m, n) for(ll i = (m); i >= (n); --i)
#define rep(i, n) REP(i, 0, n)
#define repn(i, n) REPN(i, 1, n)
#define repr(i, n) REPR(i, n, 0)
#define repnr(i, n) REPNR(i, n, 1)
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define fs first
#define sc second
template <typename T>
bool chmax(T &a, const T b){if(a < b){a = b; return true;} return false;}
template <typename T>
bool chmin(T &a, const T b){if(a > b){a = b; return true;} return false;}
template <typename T>
ll pow2(const T n){return (1LL << n);}
template <typename T>
void cosp(const T n){cout << n << ' ';}
void co(void){cout << '\n';}
template <typename T>
void co(const T n){cout << n << '\n';}
template <typename T1, typename T2>
void co(pair<T1, T2> p){cout << p.fs << ' ' << p.sc << '\n';}
template <typename T>
void co(const Vec1<T> &v){for(T i : v) cosp(i); co();}
template <typename T>
void co(initializer_list<T> v){for(T i : v) cosp(i); co();}
void ce(void){cerr << '\n';}
template <typename T>
void ce(const T n){cerr << n << '\n';}
template <typename T>
void cesp(const T n){cerr << n << ' ';}
template <typename T>
void ce(initializer_list<T> v){for(T i : v) cesp(i); ce();}
void sonic(){ios::sync_with_stdio(false); cin.tie(0);}
void setp(const ll n){cout << fixed << setprecision(n);}
constexpr int INF = 1e9+1;
constexpr ll LINF = 1e18+1;
// constexpr ll MOD = 1e9+7;
constexpr ll MOD = 998244353;
constexpr ld EPS = 1e-11;
const double PI = acos(-1);

using CP = complex<double>;

void fft(vector<CP> &a, bool inv){
	int n = a.size();
	if (n == 1) return;
	vector<CP> even(n / 2), odd(n / 2);
	for (int i = 0; i < n / 2; i++) {
		even[i] = a[2 * i];
		odd[i] = a[2 * i + 1];
	}
	fft(even, inv);
	fft(odd, inv);
	CP omega = polar(1.0, (-2 * inv + 1) * 2 * PI / n);
	CP pow_omega = 1.0;
	for (int i = 0; i < n / 2; i++) {
		a[i] = even[i] + pow_omega * odd[i];
		a[i + n / 2] = even[i] - pow_omega * odd[i];
		pow_omega *= omega;
	}
}

vector<CP> conv(vector<CP> &a, vector<CP> &b){
	int n = a.size() + b.size();
	int N = 1;
	while (N <= n) N <<= 1;

	a.resize(N);
	b.resize(N);

	fft(a, false);
	fft(b, false);

	vector<CP> res(N);
	for (int i = 0; i < N; ++i) {
		res[i] = a[i] * b[i] / CP(N);
	}

	fft(res, true);
	return res;
}

int main(void){
	ll n, m;
	cin >> n >> m;
	Vec a(100001);
	rep(i, n) {
		ll t;
		cin >> t;
		a[t]++;
	}
	vector<CP> b(100001);
	rep(i, 100001) b[i] = {a[i], 0};
	vector<CP> c = b;

	auto v = conv(b, c);

	ll ans = 0, rest = m;
	repr(i, v.size()) {
		ll t = v[i].real() + 0.5;
		ans += i * min(t, rest);
		rest -= min(t, rest);
		if (!rest) break;
	}
	co(ans);

	return 0;
}


Measured memory_bytes: 24952