n = int(input())
a = list(map(int,input().split()))
b = list(map(int,input().split()))
sa = sum(a)
sb = sum(b)
if n == 2:
    dif = a[0]-b[0]
    if a[1]+dif == b[1]:
        print(abs(dif))
    else:
        print(-1)
    exit()
if sb > sa or (sa-sb)%(n-2) != 0:
    print(-1)

else:
    count = (sa-sb)//(n-2)
    
    x = 0
    for i in range(n):
        dif = a[i]-b[i]
        
        if dif == count:
            continue
        if dif >= 0:
            if (count-dif)%2:
                print(-1)
                exit()
            x += (count-dif)//2
        else:
            if (count+dif)%2:
                print(-1)
                exit()
            x += -dif + (count+dif)//2
        
    if x == count:
        print(count)
    else:
        print(-1)