Problem10765--ABC140 - E - Second Sum

10765: ABC140 - E - Second Sum

[Creator : ]
Time Limit : 1.000 sec  Memory Limit : 512 MiB

Description

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

Input

Input is given from Standard Input in the following format:

```
$N$
$P_1$ $P_2$ $\ldots$ $P_N$
```

Output

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

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.

Sample 1 Input

3
2 3 1

Sample 1 Output

5

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

Sample 2 Input

5
1 2 3 4 5

Sample 2 Output

30

Sample 3 Input

8
8 2 7 3 4 5 6 1

Sample 3 Output

136

Source/Category