N = int(input())
lsA = list(map(int,input().split()))
lsB = list(map(int,input().split()))
ls = []
for i in range(N):
    ls.append(lsA[i]-lsB[i])
if N == 2:
    if sum(lsA) != sum(lsB):
        print(-1)
        exit()
    print(abs(lsA[0]-lsB[0]))
    exit()
if sum(ls) % (N-2) != 0:
    print(-1)
    exit()
kai = sum(ls)//(N-2)
for i in range(N):
    ls[i] -= kai
cnt = 0
for i in range(N):
    if ls[i] % 2 != 0:
        print(-1)
        exit()
    if ls[i] > 0:
        print(-1)
        exit()
    cnt += -ls[i]//2
    if cnt > kai:
        print(-1)
        exit()
print(kai)