import os
import sys
from io import BytesIO, IOBase

BUFSIZE = 8192


class FastIO(IOBase):
	newlines = 0
	
	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = "x" in file.mode or "r" not in file.mode
		self.write = self.buffer.write if self.writable else None
	
	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
		self.newlines = 0
		return self.buffer.read()
	
	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b"\n")+(not b)
			ptr = self.buffer.tell()
			self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
		self.newlines -= 1
		return self.buffer.readline()
	
	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s:self.buffer.write(s.encode("ascii"))
		self.read = lambda:self.buffer.read().decode("ascii")
		self.readline = lambda:self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda:sys.stdin.readline().rstrip("\r\n")

n = int(input())
ikeru = [[] for i in range(n)]

for i in range(n-1):
	a, b = map(int,input().split())
	a-=1; b-=1
	ikeru[a].append(b)
	ikeru[b].append(a)

c = list(map(int,input().split()))

mada = [~0, 0]
tansaku = [0] * n
tansaku[0] = 1

dp0 = [0] * n # 自分が空いている
dp1 = [0] * n # 自分が空いていない

while mada:
	i = mada.pop()
	if i >= 0:
		for j in ikeru[i]:
			if tansaku[j] == 0:
				tansaku[j] = 1
				mada.append(~j)
				mada.append(j)
	else:
		i = ~ i
		if c[i] == 1:
			r1 = 0
			r0 = 10 ** 9
		else:
			r1 = 10 ** 9
			r0 = 0
		for j in ikeru[i]:
			if tansaku[j] == 2:
				r0, r1 = min(r0 + dp1[j], r1 + dp0[j] + 1), min(r0 + dp0[j] + 1, r1 + dp1[j])
		dp1[i] = r1
		dp0[i] = r0
		tansaku[i] = 2

#print(dp0, dp1)

if dp1[0] > 10 ** 8:
	print(-1)
else:
	print(dp1[0])