#include <iostream>
#include <iomanip>
#include <string>
#include <stack>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <iterator>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <regex>
#include <complex>
using namespace std;
using pii  = pair<int,int>;
using ll=long long;
using ld=long double;
#define pb push_back
#define mp make_pair
#define sc second
#define fr first
#define stpr setprecision
#define cYES cout<<"YES"<<endl
#define cNO cout<<"NO"<<endl
#define cYes cout<<"Yes"<<endl
#define cNo cout<<"No"<<endl
#define rep(i,n) for(ll i=0;i<(n);++i)
#define Rep(i,a,b) for(ll i=(a);i<(b);++i)
#define rrep(i,n) for(int i=n-1;i>=0;i--)
#define rRep(i,a,b) for(int i=a;i>=b;i--)
#define crep(i) for(char i='a';i<='z';++i)
#define psortsecond(A,N) sort(A,A+N,[](const pii &a, const pii &b){return a.second<b.second;});
#define ALL(x) (x).begin(),(x).end()
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define endl '\n'
int ctoi(const char c){
  if('0' <= c && c <= '9') return (c-'0');
  return -1;
}
ll gcd(ll a,ll b){return (b == 0 ? a : gcd(b, a%b));}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
constexpr ll MOD=1000000007;
constexpr ll INF=1000000011;
constexpr ll MOD2=998244353;
constexpr ll LINF = 1001002003004005006ll;
constexpr ld EPS=10e-8;
template <class T, class U> inline bool chmax(T& lhs, const U& rhs) { if (lhs < rhs) { lhs = rhs; return 1; } return 0; }
template <class T, class U> inline bool chmin(T& lhs, const U& rhs) { if (lhs > rhs) { lhs = rhs; return 1; } return 0; }
template<typename T> istream& operator>>(istream& is,vector<T>& v){for(auto&& x:v)is >> x;return is;}
template<typename T,typename U> istream& operator>>(istream& is, pair<T,U>& p){ is >> p.first; is >> p.second; return is;}
template<typename T,typename U> ostream& operator>>(ostream& os, const pair<T,U>& p){ os << p.first << ' ' << p.second; return os;}
template<class T> ostream& operator<<(ostream& os, vector<T>& v){
  for(auto i=begin(v); i != end(v); ++i){
    if(i !=begin(v)) os << ' ';
    os << *i;
  }
  return os;
}

namespace FastFourierTransform
{
  using C = complex< double >;

  void DiscreteFourierTransform(vector< C > &F, bool rev)
  {
    const int N = (int) F.size();
    const double PI = (rev ? -1 : 1) * acos(-1);
    for(int i = 0, j = 1; j + 1 < N; j++) {
      for(int k = N >> 1; k > (i ^= k); k >>= 1);
      if(i > j) swap(F[i], F[j]);
    }
    C w, s, t;
    for(int i = 1; i < N; i <<= 1) {
      for(int k = 0; k < i; k++) {
        w = polar(1.0, PI / i * k);
        for(int j = 0; j < N; j += i * 2) {
          s = F[j + k];
          t = C(F[j + k + i].real() * w.real() - F[j + k + i].imag() * w.imag(),
                F[j + k + i].real() * w.imag() + F[j + k + i].imag() * w.real());
          F[j + k] = s + t, F[j + k + i] = s - t;
        }
      }
    }
    if(rev) for(int i = 0; i < N; i++) F[i] /= N;
  }

  vector< long long > Multiply(const vector< int > &A, const vector< int > &B)
  {
    int sz = 1;
    while(sz < A.size() + B.size() - 1) sz <<= 1;
    vector< C > F(sz), G(sz);
    for(int i = 0; i < A.size(); i++) F[i] = A[i];
    for(int i = 0; i < B.size(); i++) G[i] = B[i];
    DiscreteFourierTransform(F, false);
    DiscreteFourierTransform(G, false);
    for(int i = 0; i < sz; i++) F[i] *= G[i];
    DiscreteFourierTransform(F, true);
    vector< long long > X(A.size() + B.size() - 1);
    for(int i = 0; i < A.size() + B.size() - 1; i++) X[i] = F[i].real() + 0.5;
    return (X);
  }
};

vector<int> A(100001);

int main() {

  ll N,M,X,Y=0;
  cin >> N >> M;
  rep(i,N){
    cin >> X;
    A[X]++;
  }

  vector<ll> answer = FastFourierTransform::Multiply(A, A);
  ll ans=0;
  rrep(i,200001){
    if(Y+answer[i]>M){
      ans+= (M-Y)*i;
      cout << ans << endl;
      return 0;
    }
    else{
      Y+=answer[i];
      ans+=answer[i]*i;
    }
  }
  cout << ans << endl;
}

Measured memory_bytes: 10368