#!/bin/python3

import itertools

def solve(A: list, n:int):
    #  Return the sum of S(S(A)) modulo 10^9+7.
    # get S(A)
    idxpairs = sorted(itertools.combinations(range(n+1), 2), key=lambda x: x[1]-x[0])
    # print(idxpairs)
    SA = [max(A[istart:iend]) for istart, iend in idxpairs]
    # print('S(A)', list(SA))
    
    idxpairs = list(sorted(itertools.combinations(range(len(SA)+1), 2), key=lambda x: x[1]-x[0]))
    return sum(max(SA[istart:iend]) for istart, iend in idxpairs)

if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = solve(A, n)
    print(result)