#!/bin/python3

import sys
def pair(c):
    s=0
    for i in range(len(c)):
        for j in range(i+1,len(c)):
            s += c[i]*c[j]
    return s
        
def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    l=list()
    for i in range(len(A)):
        for j in range(i+1,len(A)):
            l.append(pair(A[i:j+1]))
    return max(l)
    
    
if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)