#include <bits/stdc++.h>
#define BIT(n) (1LL << (n))
#define BITF(n, i) (((n) >> i) & 1)
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define REPI(i, x) for (int i = 1; i <= x; i++)
#define FORI(i, m, n) for (int i = m; i <= n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define REPZ(i, x) for (int i = 0; i <= x; i++)
#define FORA(i, n) for (auto &&i : n)
using namespace std;
#define DUMPOUT cerr
// vector
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec) is >> x;
  return is;
}
// pair
template <typename T, typename U> ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}
// vector
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "{";
  REP(i, (int)vec.size())
  os << vec[i] << (i + 1 == (int)vec.size() ? "" : ", ");
  os << "}";
  return os;
}
// map
template <typename T, typename U> ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "{";
  FORA(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end()) os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
// set
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "{";
  FORA(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end()) os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head &&head, Tail &&... tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0) DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define DUMP(...)                                                             \
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                             \
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl \
          << "    ",                                                          \
      dump_func(__VA_ARGS__)
#define PRINTARR(x, y)                                     \
  cerr << #x << "=\n";                                     \
  for (auto itr = x; itr != y; itr++) cerr << *itr << " "; \
  cerr << endl;
#define PRINTARR2(x, i0, i1)                                       \
  cerr << #x << "=\n";                                             \
  for (int ii0 = 0; ii0 < i0; ii0++) {                             \
    for (int ii1 = 0; ii1 < i1; ii1++) cerr << x[ii0][ii1] << " "; \
    cerr << endl;                                                  \
  }
#else
#define DEB if (false)
#define DUMP(...)
#define PRINTARR(x, y)
#define PRINTARR2(x, i0, i1)
#endif
#define ALL(v) v.begin(), v.end()
#define fst first
#define snd second
#define mp make_pair
#define pb push_back
#define epb emplace_back
#define int long long
#define pint pair<int, int>
#define ld long double
using namespace std;
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 (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> using vec = std::vector<T>;
template <class T> void print(const T &x) { cout << x << "\n"; }
const int MOD = 1000000007, INF0 = 1061109567, INF = INF0 * INF0;
const double EPS = 1e-10, PI = acos(-1.0);
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

#define MAXSIZE (1 << 22)
// Cooley–Tukey FFT algorithm O(N log N) 配列ver
void fft(double *a0, double *a1, int n, bool inverse = false) {
  int h = 0;  // h = log_2(n)
  for (int i = 0; 1 << i < n; i++) h++;
  // バタフライ演算用の配置入れ替え
  for (int i = 0; i < n; i++) {
    int j = 0;
    for (int k = 0; k < h; k++) j |= (i >> k & 1) << (h - 1 - k);
    if (i < j) {
      swap(a0[i], a0[j]);
      swap(a1[i], a1[j]);
    }
  }
  // バタフライ演算
  for (int b = 1; b < n; b *= 2) {
    // 第 log_2(b) + 1 段
    // ブロックサイズ = b * 2
    for (int j = 0; j < b; j++) {
      // ブロック内 j 個目
      // 重み w = (1 の原始 2b 乗根の j 乗)
      double theta = (2 * M_PI) / (2 * b) * j * (inverse ? 1 : -1);
      double w0 = cos(theta);
      double w1 = sin(theta);

      for (int k = 0; k < n; k += b * 2) {
        // k を先頭とするブロック
        double s0 = a0[j + k];                                // 前
        double s1 = a1[j + k];                                // 前
        double t0 = a0[j + k + b] * w0 - a1[j + k + b] * w1;  // 後
        double t1 = a0[j + k + b] * w1 + a1[j + k + b] * w0;  // 後
        a0[j + k] = s0 + t0;                                  // 前の更新
        a1[j + k] = s1 + t1;                                  // 前の更新
        a0[j + k + b] = s0 - t0;                              // 後の更新
        a1[j + k + b] = s1 - t1;                              // 後の更新
      }
    }
  }
  // 逆変換時にサイズで割る調整
  if (inverse)
    for (int i = 0; i < n; i++) a0[i] /= n, a1[i] /= n;
}

// FFT による畳み込み O(N log N)
double fftA[MAXSIZE];
double fftB[MAXSIZE];
void convolve2(double *a, int n) {
  int s = n + n - 1;  // 畳み込み結果のサイズ
  int t = 1;          // FFT に使う配列のサイズ（2 の累乗）
  while (t < s) t *= 2;
  fill(fftA, fftA + t, 0);
  fft(a, fftA, t);
  //  PRINTARR(fftA, fftA + t);
  for (int i = 0; i < t; i++) {
    double tmpa = a[i];
    a[i] = a[i] * a[i] - fftA[i] * fftA[i];  // 畳み込み結果の FFT 結果を得る
    fftA[i] = 2 * tmpa * fftA[i];
  }
  fft(a, fftA, t, true);  // IFFT で畳み込み結果を得る
}

#define MAXN 400400

/*
[&] { return; }();下のスラッシュを2つ追加しただけ.上のスラッシュを2つにすれば外れる.
//*/

int N, M;
double aa[MAXN];
signed main() {
  cin.tie(0), ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);

  cin >> N >> M;
  int maxV = 0;
  REP(i, N) {
    int p;
    cin >> p;
    chmax(maxV, p);
    aa[p]++;
  }
  // PRINTARR(aa, aa + (maxV + 1));
  DUMP(maxV);
  convolve2(aa, maxV + 1);
  // PRINTARR(aa, aa + 2 * (maxV + 1));

  int ans = 0;
  REPR(i, 2 * maxV) {
    int val = round(aa[i]);
    //  DUMP(i, val);
    if (val >= 1) {
      DUMP(i, val);
      int ret = min(val, M);
      M -= ret;
      ans += i * ret;
      DUMP(M, i, ret, ans);
    }
    if (M == 0) break;
  }
  print(ans);
}

Measured memory_bytes: 8448