Problem:
Score : 500 points

Problem Statement

Takahashi has come to a party as a special guest.
There are N ordinary guests at the party. The i-th ordinary guest has a power of A_i.

Takahashi has decided to perform M handshakes to increase the happiness of the party (let the current happiness be 0).
A handshake will be performed as follows:

Takahashi chooses one (ordinary) guest x for his left hand and another guest y for his right hand (x and y can be the same).

Then, he shakes the left hand of Guest x and the right hand of Guest y simultaneously to increase the happiness by A_x+A_y.

However, Takahashi should not perform the same handshake more than once. Formally, the following condition must hold:

Assume that, in the k-th handshake, Takahashi shakes the left hand of Guest x_k and the right hand of Guest y_k. Then, there is no pair p, q (1 \leq p < q \leq M) such that (x_p,y_p)=(x_q,y_q).

What is the maximum possible happiness after M handshakes?

Constraints

1 \leq N \leq 10^5

1 \leq M \leq N^2

1 \leq A_i \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N M
A_1 A_2 ... A_N

Output

Print the maximum possible happiness after M handshakes.

Sample Input 1

5 3
10 14 19 34 33

Sample Output 1

202

Let us say that Takahashi performs the following handshakes:

In the first handshake, Takahashi shakes the left hand of Guest 4 and the right hand of Guest 4.

In the second handshake, Takahashi shakes the left hand of Guest 4 and the right hand of Guest 5.

In the third handshake, Takahashi shakes the left hand of Guest 5 and the right hand of Guest 4.

Then, we will have the happiness of (34+34)+(34+33)+(33+34)=202.

We cannot achieve the happiness of 203 or greater, so the answer is 202.

Sample Input 2

9 14
1 3 5 110 24 21 34 5 3

Sample Output 2

1837

Sample Input 3

9 73
67597 52981 5828 66249 75177 64141 40773 79105 16076

Sample Output 3

8128170

Solution in Python (3.4.3) (judge verdict: Runtime Error)

temp = input().split()
n, m = int(temp[0]), int(temp[1])

temp = input().split()
guest = []
for i in range(n):
    guest.append(int(temp[i]))

guest.sort(reverse=True)

flag = 0


def for_i():
    ans = 0
    dz = 0
    zz = 0
    for i in range(len(guest)):
        if dz+(n-(i+1))*2+1 < m:
            dz += (n-(i+1))*2+1
            zz += 1
        else:
            break

    for i in range(zz+1):
        ans += guest[i]*2
        if i == zz:
            z = (m-dz-1)/2
            for j in range(i+1, i+1+z):
                # print("i:{} j:{}".format(i, j))
                ans += (guest[i]+guest[j])*2
            return i, j, ans
        else:
            for j in range(i+1, len(guest)):
                ans += (guest[i]+guest[j])*2


i, j, ans = for_i()
if (m-1) % 2 == 1:
    ans += guest[i] + guest[j+1]

print(ans)