#!/bin/python

import sys

def largestValue(a):
    n=len(a)
    z=0
    for i in xrange(n):
        q=[a[i]]
        for j in xrange(i+1,n):
            q.append(a[j])
            z=max(z,sum(i[0]*i[1] for i in combinations(q,2)))
    return z
if __name__ == "__main__":
    from itertools import combinations
    from sys import stdin
    n = int(stdin.readline().strip())
    A = map(int,stdin.readline().split())
    result = largestValue(A)
    print result