n = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

if sum(A) >= sum(B):
    print(-1)
    exit()
D = []
for i in range(n):
    D.append(B[i] - A[i])
sumD = sum(D)
if n == 2:
    if sumD == 0:
        print(abs(D[0]))
    else:
        print(-1)
elif sumD < 0 and abs(sumD) % (n - 2) == 0:
    cnt = abs(sumD) // (n - 2)
    res = 0
    for i in range(n):
        if D[i] + cnt < 0 or (D[i] + cnt) % 2 != 0:
            print(-1)
            exit()
        res += (D[i] + cnt) // 2
    if res == cnt:
        print(cnt)
    else:
        print(-1)
else:
    print(-1)