n=int(input())
a=list(map(int,input().split()))
b=list(map(int,input().split()))
if n==2:
  if sum(a)==sum(b):print(abs(a[0]-b[0]))
  else:print(-1)
  exit()
if sum(a)<sum(b) or (sum(a)-sum(b))%(n-2)!=0:exit(print(-1))
ans=(sum(a)-sum(b))//(n-2)
c=[b[i]-a[i]+ans for i in range(n)]
d=[0]*n
for i in range(n):
  if c[i]<0:exit(print(-1))
  if c[i]%2==1:exit(print(-1))
  d[i]=c[i]//2
if sum(d)==ans:print(ans)
else:print(-1)