Link bài: https://lqdoj.edu.vn/problem/absmax

l = input()
sq = list(map(int, input().split()))

sq.sort()
a = sq[0]
b = sq[1]
c = sq[-1]
d = sq[-2]

if abs(a+b) > abs(c+d):
print(abs(a+b))
else:
print(abs(c+d))