#include <bits/stdc++.h>
#define REP(i, n)     for(int i = 0;i < n;i++)
#define REPR(i, n)    for(int i = n;i >= 0;i--)
#define FOR(i, m, n)  for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define VRSORT(v) sort(v.begin(), v.end(),greater<int>());
#define ALL(X) (X).begin(),(X).end()
#define INF 99999999
#define M_PI 3.14159265358979323846
#define MOD 1000000007

#ifdef __LOCAL
    #define DBG(X) cout << #X << " = " << (X) << endl;
    #define SAY(X) cout << (X) << endl;
#else
    #define DBG(X)
    #define SAY(X)
#endif

#ifdef __LOCAL
    #include <filesystem>
    namespace fs = std::filesystem;
#endif

using namespace std;

using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

int dx[]={1, 0, -1, 0, 0};
int dy[]={0, 1, 0, -1, 0};
const int INT_INF = (int)(2e9);
const ll  LL_INF = (ll)(2e18);
const int NIL = -1;
static mt19937 _g(time(nullptr));
 
std::string pad(int num){ char buffer[4]; std::snprintf(buffer, sizeof(buffer), "%03d", num); return buffer;}
inline ll randint(ll a, ll b) { ll w = (_g() << 31LL) ^ _g(); return a + w % (b - a + 1); }
inline void fast_io() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); };
template<typename T> inline T sign(T x) { return T(x > 0) - T(x < 0); }
template<typename T, typename S> inline ostream& operator<<(ostream& os, const pair<T, S> p) { cout << "[" << p.first << ";" << p.second << "]"; return os; }
template<typename T> inline ostream& operator<<(ostream& os, const vector<T>& v) { for (auto el : v) os << el << " "; return os; }
template<typename T, typename S> inline ostream& operator<<(ostream& os, const map<T,S>& v) { for (auto el : v) os << el << " "; return os; }
template<typename T> inline T fetch() { T ret; cin >> ret; return ret; }
template<typename T> inline vector<T> fetch_vec(int sz) { vector<T> ret(sz); for (auto& elem : ret) cin >> elem; return ret; }

ll N,M;
vector<ll> A,AS;
void input(){
  #ifdef __LOCAL
      fs::path p = __FILE__;
      fs::path input,output;
      input = output = p.parent_path();
      input += string("/input/") + string(p.stem()) + string(".txt");
      output += string("/output/") + string(p.stem()) + string(".txt");
      freopen(input.c_str(), "r", stdin);
      freopen(output.c_str(), "w", stdout);
  #endif

  fast_io();
  cin >> N >> M;
  A = fetch_vec<ll>(N);
  VSORT(A)
  AS.assign(N+1,0LL);
  AS[0] = 0;
  for (ll i = 0; i < N; i++)
  {
      AS[i+1] =AS[i]+A[i];
  }
  DBG(A)
  
}

// 握手した時の幸福度がｘ以上になるペアの数。
ll countHappines(ll x){
    ll res=0;
    for (ll i = 0; i < N; i++)
    {
        ll rest = (x-A[i]);
        auto itr = lower_bound(A.begin(),A.end(),rest);
        ll n = A.end()-itr;
        res += n;        
    }
    DBG(x)
    DBG(res)
    return res;
}

int solve(){
    ll ok=0;
    ll ng=1e8;
    while(ng-ok>1){
        ll mid = (ok+ng)/2;
        if(countHappines(mid)>=M) ok=mid;
        else ng=mid;
    }
    DBG(ok)
    ll ans=0;
    ll dbgM=0;
    for (ll i = 0; i < N; i++)
    {
        ll rest = ng-A[i];
        DBG(A[i])
        DBG(rest)
        auto itr = lower_bound(A.begin(),A.end(),rest);
        ll idx = itr-A.begin();
        DBG(idx)
        dbgM += N-idx;
        ans += A[i]*(N-idx);
        ans += AS[N] - AS[idx];
        DBG(ans)
    }
    DBG(dbgM)
    ll reCount=M-dbgM;
    if(reCount>0) ans += reCount*ok;
    // if(reCount>0){
    //     for (ll i = 0; i < N; i++)
    //     {
    //         ll rest = ok-A[i];
    //         auto itr = lower_bound(A.begin(),A.end(),rest);
    //         ll idx = itr-A.begin();
    //         if(reCount<N-idx){
    //             ans -= A[i]*reCount;
    //             ans -= AS[N] - AS[N-reCount];
    //             reCount -= (N-idx);
    //         }
    //         else{
    //             ans -= A[i]*(N-idx);
    //             ans -= AS[N] - AS[idx];
    //             reCount -= (N-idx);
    //         }
    //         DBG(ans)
    //         if(reCount<=0) break;
    //     }
    // }
    cout << ans << endl;    
    return 0;
}

int main()
{
  input();
  solve();
  return 0;
}


Measured memory_bytes: 1792