Score: 500 points
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 is given from Standard Input in the following format:
N P_1 P_2 \ldots P_N
Print \displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}.
3 2 3 1
5
X_{1, 2} = 2, X_{1, 3} = 2, and X_{2, 3} = 1, so the sum is 2 + 2 + 1 = 5.
5 1 2 3 4 5
30
8 8 2 7 3 4 5 6 1
136