#include <bits/stdc++.h>
//#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
//#include "boost/multiprecision/cpp_int.hpp"
//typedef boost::multiprecision::cpp_int LL;
typedef long double dd;
//#define i_7 (ll)(1E9+7)
#define i_7 998244353
#define i_5 i_7-2

ll mod(ll a){
    ll c=a%i_7;
    if(c>=0)return c;
    return c+i_7;
}
typedef pair<ll,ll> l_l;
typedef pair<dd,dd> d_d;
ll inf=(ll)1E16;
#define rep(i,l,r) for(ll i=l;i<=r;i++)
#define pb push_back
ll max(ll a,ll b){if(a<b)return b;else return a;}
ll min(ll a,ll b){if(a>b)return b;else return a;}
void Max(ll &pos,ll val){pos=max(pos,val);}//Max(dp[n],dp[n-1]);
void Min(ll &pos,ll val){pos=min(pos,val);}
void Add(ll &pos,ll val){pos=mod(pos+val);}
dd EPS=1E-9;
#define fastio ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define fi first
#define se second
#define endl "\n"
#define SORT(v) sort(v.begin(),v.end())
#define ERASE(v) v.erase(unique(v.begin(),v.end()),v.end())
#define POSL(v,x) (lower_bound(v.begin(),v.end(),x)-v.begin())
#define POSU(v,x) (upper_bound(v.begin(),v.end(),x)-v.begin())
//template<class T>void max(T a,T b){if(a<b)return b;else return a;}
//template<class T>void min(T a,T b){if(a>b)return b;else return a;}
//template<class T>bool Max(T&a, T b){if(a < b){a = b;return 1;}return 0;}
//template<class T>bool Min(T&a, T b){if(a > b){a = b;return 1;}return 0;}

//////////////////////////

using Complex = complex<double>;
vector<Complex> dft(vector<Complex> A, int N, int sgn = 1) {
    if(N == 1) return A;
 
    vector<Complex> F(N / 2), G(N / 2);
    for(int i=0; i<N/2; i++) {
        F[i] = A[2 * i + 0];
        G[i] = A[2 * i + 1];
    }
 
    F = dft(F, N / 2, sgn);
    G = dft(G, N / 2, sgn);
 
    Complex zeta(cos(2.0 * M_PI / N), sin(2.0 * M_PI / N) * sgn);
    Complex pow_zeta = 1;
 
    for(int i=0; i<N; i++) {
        A[i] = F[i % (N / 2)] + pow_zeta * G[i % (N / 2)];
        pow_zeta *= zeta;
    }
    return A;
}
 
vector<Complex> inv_dft(vector<Complex> A, int N) {
    A = dft(A, N, -1);
    for(int i=0; i<N; i++) {
        A[i] /= N;
    }
    return A;
}
 
vector<Complex> multiply(vector<Complex> A, vector<Complex> B) {
    int sz = A.size() + B.size() + 1;
    int N = 1; while(N < sz) N *= 2;
 
    A.resize(N), B.resize(N);
    A = dft(A, N);
    B = dft(B, N);
 
    vector<Complex> F(N);
    for(int i=0; i<N; i++) {
        F[i] = A[i] * B[i];
    }
    return inv_dft(F, N);
}
////////////////////////////

#define N 100005
vector<Complex>A(N);

int main(){fastio
    ll n,m;cin>>n>>m;
    
    rep(i,1,n){
        ll a;cin>>a;
        A[a]+=1;
    }
    vector<Complex>B=multiply(A,A);
    
    ll ans=0;
    for(ll i=N*2-2;i>=0;i--){
        ll t=(ll)(B[i].real()+0.5);
        if(t<m){
            m-=t;
            ans+=t*i;
        }else{
            ans+=m*i;break;
        }
    }
    
    
    cout<<ans<<endl;
    return 0;
}
/*
int main()
    int N; scanf("%d", &N);
 
    vector<Complex> A(N+1), B(N+1);
    A[0] = B[0] = Complex(0);
    for(int i=1; i<=N; i++) {
        int vl, vr; scanf("%d%d", &vl, &vr);
        A[i] = Complex(vl);
        B[i] = Complex(vr);
    }
 
    vector<Complex> ans = multiply(A, B);
    for(int i=1; i<=2*N; i++) {
        printf("%d\n", (int)(ans[i].real() + 0.5));///////////////こうやって使う
    }
    return 0;

*/


Measured memory_bytes: 36684