#!/bin/ruby

def largestValue(a)
    m = false
    
    for i in (0...a.size)
        for j in (i + 1...a.size)
            s = 0
            for p in (i..j)
                for q in (p + 1..j)
                    s += a[p] * a[q]
                end
            end
            if !m || s > m
                m = s
            end
        end
    end      
    
    m
end

n = gets.strip.to_i
a = gets.strip
a = a.split(' ').map(&:to_i)
result = largestValue(a)
puts result