#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll MOD=1000000007;


int main (){   
    int N;
  	ll M;
 	cin >> N >> M;
    vector<ll> A(N);
    for (auto& x : A) cin >> x;
    sort(A.begin(), A.end());
    ll pass = 0, fail = 2 * 1e5 + 10;
    while (fail - pass > 1) {
      ll X = (pass + fail) / 2;
      ll cnt = 0;
      for (int i = 0, j = N - 1; i < N; i++) {
        while (j >= 0 && A[i] + A[j] >= X) --j;
        cnt += N - j - 1;
      }
      if (cnt >= M) {
        pass = X;
      } else {
        fail = X;
      }
    }
    ll res = 0;
    ll sum = 0, rem = M;
    for (int i = 0, j = N - 1; i < N; i++) {
      while (j >= 0 && A[i] + A[j] > pass) {
        sum += A[j];
        --j;
      }
      ll c = N - j - 1;
      rem -= c;
      res += sum + c * A[i];
    }
    res += pass * rem;
    cout << res << endl;
  
 
}


