#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll,ll>
#define FOR(I,A,B) for(ll I = int(A); I < int(B); ++I)
#define FORR(I,A,B) for(ll I = int((B)-1); I >= int(A); --I)
#define TO(x,t,f) ((x)?(t):(f))
#define SORT(x) (sort(x.begin(),x.end())) // 0 2 2 3 4 5 8 9
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin()) //xi>=v  x is sorted
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin()) //xi>v  x is sorted
#define NUM(x,v) (POSU(x,v)-POSL(x,v))  //x is sorted
#define REV(x) (reverse(x.begin(),x.end())) //reverse
ll gcd(ll a,ll b){if(a<b)swap(a,b);if(a%b==0)return b;return gcd(b,a%b);}
ll lcm(ll a,ll b){ll c=gcd(a,b);return ((a/c)*(b/c)*c);}//saisyo kobaisu
#define NEXTP(x) next_permutation(x.begin(),x.end())
const ll INF=1e18+7;
const ll MOD=1e9+7;


namespace FastFourierTransform {
	using real=double;
 
	struct C {
	real x, y;
 
	C() : x(0), y(0) {}
 
	C(real x, real y) : x(x), y(y) {}
 
	inline C operator+(const C &c) const { return C(x + c.x, y + c.y); }
 
	inline C operator-(const C &c) const { return C(x - c.x, y - c.y); }
 
	inline C operator*(const C &c) const { return C(x * c.x - y * c.y, x * c.y + y * c.x); }
 
	inline C conj() const { return C(x, -y); }
	};
 
	const real PI = acosl(-1);
	int base = 1;
	vector< C > rts = {{0, 0},
					 {1, 0}};
	vector< int > rev = {0, 1};
 
 
	void ensure_base(int nbase) {
	if(nbase <= base) return;
	rev.resize(1 << nbase);
	rts.resize(1 << nbase);
	for(int i = 0; i < (1 << nbase); i++) {
		rev[i] = (rev[i >> 1] >> 1) + ((i & 1) << (nbase - 1));
	}
	while(base < nbase) {
		real angle = PI * 2.0 / (1 << (base + 1));
		for(int i = 1 << (base - 1); i < (1 << base); i++) {
		rts[i << 1] = rts[i];
		real angle_i = angle * (2 * i + 1 - (1 << base));
		rts[(i << 1) + 1] = C(cos(angle_i), sin(angle_i));
		}
		++base;
	}
	}
 
	void fft(vector< C > &a, int n) {
	assert((n & (n - 1)) == 0);
	int zeros = __builtin_ctz(n);
	ensure_base(zeros);
	int shift = base - zeros;
	for(int i = 0; i < n; i++) {
		if(i < (rev[i] >> shift)) {
		swap(a[i], a[rev[i] >> shift]);
		}
	}
	for(int k = 1; k < n; k <<= 1) {
		for(int i = 0; i < n; i += 2 * k) {
		for(int j = 0; j < k; j++) {
			C z = a[i + j + k] * rts[j + k];
			a[i + j + k] = a[i + j] - z;
			a[i + j] = a[i + j] + z;
		}
		}
	}
	}
 
	vector< int64_t > multiply(const vector< int > &a, const vector< int > &b) {
	int need = (int) a.size() + (int) b.size() - 1;
	int nbase = 1;
	while((1 << nbase) < need) nbase++;
	ensure_base(nbase);
	int sz = 1 << nbase;
	vector< C > fa(sz);
	for(int i = 0; i < sz; i++) {
		int x = (i < (int) a.size() ? a[i] : 0);
		int y = (i < (int) b.size() ? b[i] : 0);
		fa[i] = C(x, y);
	}
	fft(fa, sz);
	C r(0, -0.25 / (sz >> 1)), s(0, 1), t(0.5, 0);
	for(int i = 0; i <= (sz >> 1); i++) {
		int j = (sz - i) & (sz - 1);
		C z = (fa[j] * fa[j] - (fa[i] * fa[i]).conj()) * r;
		fa[j] = (fa[i] * fa[i] - (fa[j] * fa[j]).conj()) * r;
		fa[i] = z;
	}
	for(int i = 0; i < (sz >> 1); i++) {
		C A0 = (fa[i] + fa[i + (sz >> 1)]) * t;
		C A1 = (fa[i] - fa[i + (sz >> 1)]) * t * rts[(sz >> 1) + i];
		fa[i] = A0 + A1 * s;
	}
	fft(fa, sz >> 1);
	vector< int64_t > ret(need);
	for(int i = 0; i < need; i++) {
		ret[i] = llround(i & 1 ? fa[i >> 1].y : fa[i >> 1].x);
	}
	return ret;
	}
};

int main(){
	ll n,m;
	cin >> n >> m;
	vector<int> a(n),A(100001,0),B(100001,0);
	FOR(i,0,n) cin>>a[i];
	FOR(i,0,n) A[a[i]]++;
	FOR(i,0,n) B[a[i]]++;
	auto s = FastFourierTransform::multiply(A, B);
	FOR(i,0,n){
		//s[2*a[i]]--;
	}
	ll ans = 0;
	for(int i=200000;i>=0;i--){
		if(s[i]>=m){
			ans += i*m;
			m = 0;
		}else if(m>=s[i]){
			m -= s[i];
			ans += i*s[i];
		}
	}
	cout << ans << endl;
}	

Measured memory_bytes: 12172