n = int(input())
a = list(map(int, input().split()))

if n == 0:
    print(0)
    exit()

left_max = [0] * n
left_max[0] = a[0]
for i in range(1, n):
    left_max[i] = max(left_max[i-1], a[i])

right_max = [0] * n
right_max[-1] = a[-1]
for i in range(n-2, -1, -1):
    right_max[i] = max(right_max[i+1], a[i])

total = 0
for i in range(n):
    current_max = max(left_max[i], right_max[i])
    total += max(abs(a[i]), abs(current_max))

print(total)