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


diff = 0
for i in range(n):
    diff += a[i] - b[i]

if diff % (n - 2) == 0 and diff // (n - 2) > 0:
    cnt = diff // (n - 2)
else:
    print(-1)
    exit()

for i in range(n):
    d = cnt - (a[i] - b[i])
    if d % 2 == 0 and d >= 0:
        continue
    else:
        print(-1)
        exit()
print(cnt)