Problem:
Score: 500 points

Problem Statement

Given is a permutation P of \{1, 2, \ldots, N\}.

For a pair (L, R) (1 \le L \lt R \le N), let X_{L, R} be the second largest value among P_L, P_{L+1}, \ldots, P_R.

Find \displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}.

Constraints

2 \le N \le 10^5

1 \le P_i \le N

P_i \neq P_j (i \neq j)

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
P_1 P_2 \ldots P_N

Output

Print \displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}.

Sample Input 1

3
2 3 1

Sample Output 1

5

X_{1, 2} = 2, X_{1, 3} = 2, and X_{2, 3} = 1, so the sum is 2 + 2 + 1 = 5.

Sample Input 2

5
1 2 3 4 5

Sample Output 2

30

Sample Input 3

8
8 2 7 3 4 5 6 1

Sample Output 3

136

Solution in PyPy3 (2.4.0) (judge verdict: Runtime Error)


def main():

    from bisect import *
    N = int(input())
    P = list(map(int, input().split()))

    index = [-1]*N
    for i in range(N):
        index[P[i]-1] = i


    q = [-1, -1, index[-1], N, N]
    ans = 0
    for i in range(N-1):
        ind = index[-2-i]
        insertion = bisect_left(q, ind)
        ans += ((q[insertion+1]-q[insertion])*(ind-q[insertion-1]) + (q[insertion]-ind)*(q[insertion-1]-q[insertion-2])) * (N-1-i)
        q.insert(insertion, ind)

    print(ans)

if __name__ == "__main__":
    main()