I,R=input,range
def S(n):
	return abs(int(n)-1)
def J():
	return map(S,I().split())
N=int(I())
E=[set()for i in R(N)]
for i in R(N-1):
	a,b=J()
	E[a].add(b),E[b].add(a)
C=list(J())
A=[0]*N
S=[0]*N
L=set()
for i in R(N):
	if len(E[i])<2:L.add(i)
while len(L):
	M=set()
	for i in L:
		if len(E[i]):
			j=E[i].pop()
			S[j]+=C[i]
			A[j]+=A[i]
			E[j].remove(i)
			M.add(j)
	for j in M:
		A[j]+=S[j]
		C[j]=(C[j]+S[j])%2
	L=M
print([A[j],-1][C[j]])