#include <bits/stdc++.h>
#include <boost/algorithm/string/join.hpp>
#include <boost/range/irange.hpp>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using boost::irange;
using boost::algorithm::join;

typedef long long ll;
typedef unsigned long long ull;
//typedef long double ld;

typedef map<int, int> mii;
typedef pair<int, int> pii;
typedef pair<double,double> pdd;
typedef set<int> si;
typedef set<ll> sll;
typedef vector<int> vi;
typedef vector<pair<int, int > > vii;
typedef vector<ll> vll;
typedef vector<double> vd;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
typedef vector<vll> vvll;

constexpr ll MOD = 1e9+7;
template<typename T>constexpr auto inf=numeric_limits<T>::max()/4;
constexpr int INF=inf<int>;
constexpr ll LINF=inf<ll>;

#define Sort(x) sort(begin(x),end(x))
#define Reverse(x) reverse(begin(x),end(x))
#define ABS(a,b) ((a)<(b)?(b)-(a):(a)-(b))
#define nbit(n) (1ull<<(n))
#define _ol3(_1,_2,_3,name,...)name
#define _rep(i,n)_repi(i,0,n)
#define _repi(i,a,b)for(int i=a,i##_l=(b);i<i##_l;++i)
#define REP(...) _ol3(__VA_ARGS__,_repi,_rep,)(__VA_ARGS__)
#define REPR(i,n) for(int i=n-1;i>=0;--i)
#define REPA(i,v) REP(i,(v).size())

// sort(begin(x), end(x), greater<ll>());
// lower_bound(a.begin(), a.end(), val): a[i] ≥ valである最左の位置
// upper_bound(a.begin(), a.end(), val): a[i] > valである最左の位置

// Returns minimum of a and b.
// If a is less b, a is set to b.
template<typename T>
T chmin(T& a, T b) {
  if (a > b) {
    a = b;
  }
  return a;
}

// Returns maximum of a and b.
// If a is less b, a is set to b.
template<typename T>
T chmax(T& a, T b) {
  if (a < b) {
    a = b;
  }
  return a;
}

template <typename T>
void dumpContents(const T& v, const string& msg)
{
  cerr << "### " << msg << " ###\n";
  for (const auto& x : v) {
    cerr << x << " ";
  }
  cerr << endl;
}

struct before_main_function {
  before_main_function() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout<<setprecision(20)<<fixed;
    #define endl "\n"
  }
} before_main_function;

// ========== end of template ==========
int N;
ll M;
vll A;
vll SA;

// x点以上の握手pairの個数 O(N logN)
ll bs(const ll x) {
  ll ret = 0;

  REP(i, N) {
    ll a = A[i];
    if (a>=x) {
      ret += N;
      continue;
    }

    ll b = x-a; // 残りb以上
    auto it = lower_bound(begin(A), end(A), b);
    ret += distance(it, end(A));
  }

  return ret;
}

int main(int argc, char** argv) {
  cin >> N >> M;
  A.resize(N);
  for (auto& a : A) {
    cin >> a;
  }
  Sort(A);

  // 累和
  SA.resize(N);
  SA[0] = A[0];
  for (int i=1; i<N; i++) {
    SA[i] = SA[i-1]+A[i];
  }

  // 1) 1握手X点以上の個数がMとなるXを求める
  ll l = 1; // 必ずtrue (M以上)
  ll r = 1e5*2+10; // 必ずfalse

  while (true) {
    ll mx = (l+r)/2;
    if (mx == l) break;

    ll m = bs(mx);

    if (m>=M) {
      l = mx;
    } else {
      r = mx;
    }
//cerr << "l,r " << l << ", " << r << endl;
  }

  // 2) X以上の握手の合計を求める
  // タイに注意
  const ll X = l+1;
//cerr << "X " << X << endl;

  ll ret = 0;
  ll count = 0;
  REP(i, N) {
    const ll a = A[i];

    if (a>=X) {
      ret += SA[N-1] + a*N;
      count += N;
      continue;
    }

    ll b = X-a;
    auto it = lower_bound(begin(A), end(A), b);
    int j = distance(begin(A), it);
    ret += SA[N-1] - (j==0 ? 0 : SA[j-1]) + a*(N-j);
    count += N-j;
  }

  assert(count<=M);
  // タイを入れる
  ret += (M-count)*(X-1);

  cout << ret << endl;

  return 0;
}


Measured memory_bytes: 1792