N = int(input())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
SA = sum(A)
SB = sum(B)
if N==2:
    if SA==SB:
        print(abs(B[0]-A[0]))
    else:
        print(-1)
    exit()


if (SA-SB)%(N-2)==0:
    cnt = (SA-SB)//(N-2)
    temp = 0
    for i in range(N):
        if B[i]-(A[i]-cnt)<0 or (B[i]-(A[i]-cnt))%2==1:
            print(-1)
            exit()
        temp += B[i]-(A[i]-cnt)
    if temp//2==cnt:
        print(cnt)
    else:
        print(-1)
else:
    print(-1)