N = int(input())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
m = []
for i in range(N):
    m.append(A[i]-B[i])
if N == 2:
    if sum(A) != sum(B):
        print(-1)
    else:
        print(abs(A[0]-B[0]))
    exit()
sm = sum(m)
if sm % (N-2) != 0:
    print(-1)
    exit()
res = sm//(N-2)
for i in range(N):
    m[i] -= res
cnt = 0
for i in range(N):
    if m[i]%2!=0 or m[i]>0:
        print(-1)
        exit()
    cnt += -m[i]//2
    if cnt > res:
        print(-1)
        exit()
print(res)