//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <utility>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

struct rep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
struct revrep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) noexcept {
  if (a < b) {
    return b - a;
  } else {
    return a - b;
  }
}
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a) {
    a = b;
  }
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b) {
    a = b;
  }
}
template <class F> class fix_point : private F {
public:
  explicit constexpr fix_point(F &&f) : F(std::forward<F>(f)) {}

  template <class... Args>
  constexpr decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, std::forward<Args>(args)...);
  }
};
template <class F> constexpr decltype(auto) make_fix(F &&f) {
  return fix_point<F>(std::forward<F>(f));
}
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91
#include <cassert>
#include <cstddef>
#include <functional>
#include <vector>

namespace n91 {

template <class T, class Operate = std::plus<T>, class Invert = std::negate<T>>
class cumulative_sum {
public:
  using value_type = T;

private:
  using size_t = std::size_t;

  Operate oper;
  Invert inve;
  std::vector<T> prefix;

public:
  cumulative_sum() = default;
  explicit cumulative_sum(const std::vector<T> &c,
                          const Operate &oper = Operate(), const T &iden = T(),
                          const Invert &inve = Invert())
      : oper(oper), inve(inve), prefix() {
    prefix.reserve(c.size() + 1);
    prefix.push_back(iden);
    for (const T &e : c) {
      prefix.push_back(oper(prefix.back(), e));
    }
  }

  T fold(const size_t first, const size_t last) const {
    assert(first <= last);
    assert(last < prefix.size());
    return oper(inve(prefix[first]), prefix[last]);
  }
  T operator[](const size_t index) const { return fold(index, index + 1); }
};

} // namespace n91

#include <algorithm>
#include <functional>
#include <iostream>
#include <utility>
#include <vector>

namespace n91 {

void main_() {
  /*
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  //*/
  const usize n = scan<usize>();
  const u64 m = scan<u64>();
  std::vector<u64> a(n);
  for (auto &e : a) {
    std::cin >> e;
  }
  u64 ans = 0;
  std::sort(a.begin(), a.end(), std::greater<u64>());
  {
    const auto count = [&](const u64 x) {
      u64 ret = 0;
      usize k = n;
      for (const usize i : rep(0, n)) {
        while (k != 0 && a[i] + a[k - 1] < x) {
          k -= 1;
        }
        ret += k;
      }
      return ret;
    };
    u64 ng = -1, ok = a[0] + a[0] + 1;
    while (ok - ng != 1) {
      const u64 mid = (ng + ok) / 2;
      if (count(mid) <= m) {
        ok = mid;
      } else {
        ng = mid;
      }
    }
    const cumulative_sum<u64> sum(a);
    usize k = n;
    for (const usize i : rep(0, n)) {
      while (k != 0 && a[i] + a[k - 1] < ok) {
        k -= 1;
      }
      ans += sum.fold(0, k);
      ans += a[i] * k;
    }
    ans += (m - count(ok)) * ng;
  }
  std::cout << ans << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 1792