import sys
from itertools import product

def values(A):
    lt = []
    for i in range(len(A)):
        for j in range(i+1, len(A)):
                lt.append((A[i], A[j]))
    #print(lt)
    #print([x[0] * x[1] for x in lt])
    s = sum([x[0] * x[1] for x in lt])
    #print(s)
    return s
def largestValue(A):
    x = []
    for i in range(len(A)):
        x.append(values(A[i:]))
    #print(x)
    return max(x)
if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)