#ifdef LOCAL
    #define _GLIBCXX_DEBUG
    #define __clock__
#else
    #pragma GCC optimize("Ofast")
#endif
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

// tourist set
template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << '\n'; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// tourist set end

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << '\n'
#define p_yes() p("YES")
#define p_no() p("NO")
#define SZ(x) ((int)(x).size())
#define SORT(A) sort(ALL(A))
#define RSORT(A) sort(ALL(A), greater<ll>())
#define MP make_pair

void no(){p_no(); exit(0);}
void yes(){p_yes(); exit(0);}

const ll mod = 1e9 + 7;
const ll inf = 1e18;
const double PI = acos(-1);

struct AccSum{
    vector<ll> Ac;
    ll L;
    AccSum(){}
    AccSum(vector<ll> &A){
        L = A.size();
        Ac.resize(L+1);
        FOR(i, 0, L){
            Ac[i+1] = Ac[i] + A[i];
        }
    }
    // sum of [a, b]
    ll sum(ll a, ll b){
        if(a<0) return -1;
        if(b>L-1) return -1;
        return Ac[b+1] - Ac[a];
    }
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N, M;
    cin >> N >> M;

    VI A(N);
    rep(i, N){
      cin >> A[i];
    }
    SORT(A);

    // debug(A);
    // for(ll a : A){
    //   for(ll b : A){
    //     cout << '(' << a << ',' << b << "),";
    //   }
    // }
    // return 0;

    AccSum Acc(A);
    
    debug(A);

    ll left = 0; // can't　とりすぎ
    ll right = 200010; // can
    // ll right = 100; // can　とらなすぎ

    while(left+1!=right){
      ll center = (left+right)/2;
      
      ll cnt=0;
      for(ll a : A){
        ll x = center - a;
        debug(x);
        auto it = lower_bound(ALL(A), x);
        ll num = distance(it, A.end());
        cnt += num;
      }

      if(cnt>M){
        // とりすぎた
        left = center;
      }else{
        right = center;
      }



      debug(cnt);
      // return 0;

      debug(center, cnt);
    }

    debug(left, right);
    ll C = left;
    ll cnt=0;
    ll sum = 0;
    for(ll a : A){
      ll x = C - a;
      debug(x);
      auto it = lower_bound(ALL(A), x);
      ll num = distance(it, A.end());
      debug(num);
      cnt += num;

      // 
      if(num>0){
        ll v = Acc.sum(N-1-num+1, N-1);
        sum += v;
        sum += a*num;
        // debug(v);

      }
    }

    debug(C);
    debug(cnt);
    debug(sum);

    if(cnt>M){
      debug("kezuru");
      ll d = cnt-M;
      debug(d);
      sum -= d*C;
    }
    p(sum);



    
    return 0;
}

Measured memory_bytes: 1792