n = gets.chomp.to_i
a0 = gets.chomp.split
if a0.size > 1
    p "assert"
    exit
end

a0 = a0[0].to_i
a_s = [a0]
(n - 1).times {
    a = gets.chomp.to_i
    a_s << a
}

def sum_of_2 l
    s = []
    l.combination(2) {|a, b|
        s << a + b
    }
    s
end

sum_s = sum_of_2 a_s
sum_s = sum_s.sort.uniq
p sum_s[-2]