#include <bits/stdc++.h>
#define whlie while
#define pb push_back
#define eb emplace
#define fi first
#define se second
#define rep(i,N) for(int i = 0; i < (N); i++)
#define repr(i,N) for(int i = (N) - 1; i >= 0; i--)
#define rep1(i,N) for(int i = 1; i <= (N) ; i++)
#define repr1(i,N) for(int i = (N) ; i > 0 ; i--)
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
using namespace std; void solve();
using ll = long long; using vl = vector<ll>;
using vi = vector<int>; using vvi = vector< vector<int> >;
constexpr int inf = 1001001001;
constexpr ll infLL = (1LL << 61) - 1;
struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(10);} } iosetupnya;
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename T, typename U> ostream& operator <<(ostream& os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<typename T, typename U> istream& operator >>(istream& is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator <<(ostream& os, const vector<T> &v) { int s = (int)v.size(); rep(i,s) os << (i ? " " : "") << v[i]; return os; }
template<typename T> istream& operator >>(istream& is, vector<T> &v) { for(auto &x : v) is >> x; return is; }
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << "\n";} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#ifdef NyaanDebug
  #include "NyaanDebug.h"
  #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0)
  #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);cout << endl;} while(0)
#else
  #define trc(...)
  #define trca(...)
  int main(){solve();}
#endif
using P = pair<string,string>; using vp = vector<P>;
constexpr int MOD = /** 1000000007; //*/ 998244353;
////////////////

void solve(){
  inl(N , M);
  vl a(N); in(a);

  sort(all(a));

  // n以上の組の個数
  auto f = [&](ll n){
    ll ret = 0;
    rep(i , N){
      ll nya = n - a[i];
      auto it = lower_bound( all(a) , nya );
      ret += (ll)(a.end() - it);
    }
    return ret;
  };

  // 閾値
  ll ng = -1 , ok = 200200 , cnt = 0;
  while(ng + 1 < ok){
    ll med = (ng + ok) / 2;
    trc(f(med) , med);
    if(f(med) <= M) ok = med , cnt = f(med);
    else ng = med; 
  }

  trc(ok);
  vl rui(N + 1);
  rep(i , N) rui[i + 1] = rui[i] + a[i];

  // 閾値 ok
  ll ans = 0;
  rep(i , N){
    ll nya = ok - a[i];
    auto it = lower_bound(all(a) , nya);
    int num = a.end() - it;
    ans += num * a[i];
    ans += rui[a.end() - a.begin()] - rui[it - a.begin()];
  }

  ans += (M - cnt) * (ok - 1);
  out(ans);

   
}

Measured memory_bytes: 1920