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)
else:
	sa=sum(A)
	sb=sum(B)
	if (sa-sb)%(N-2)!=0:
		print(-1)
		exit()
	if sa-sb<0:
		print(-1)
		exit()
	ans=(sa-sb)//(N-2)
	op=0
	for i in range(N):
		if (A[i]+ans+B[i])%2==1:
			print(-1)
			exit()
		now=(B[i]-(A[i]-ans))//2
		if now<0:
			print(-1)
			exit()
		op+=now
	if op!=ans:
		print(-1)
	else:
		print(ans)