from bisect import bisect_left

N = int(input())

G = [[] for _ in range(N)]
for _ in range(N - 1):
  u, v = [int(x) - 1 for x in input().split()]
  G[u].append(v)
  G[v].append(u)
  
S = [1 if x == '1' else -1 for x in input()]

used = [False] * N
size = [0] * N
def centroid(x):
  stk = [(x, None, 0)]
  while stk:
    u, p, t = stk.pop()
    if t == 0:
      stk.append((u, p, 1))
      for v in G[u]:
        if not used[v] and v != p:
          stk.append((v, u, 0))
    else:
      size[u] = 1 + sum(size[v] for v in G[u] if not used[v] and v != p)
  
  p = None
  while True:
    y = next((y for y in G[x] if not used[y] and y != p and size[y] * 2 > size[x]), None)
    if y is None: break
    x, p = y, x
  return x
  
def totals(x, p):
  stk = [(x, p, S[x])]
  res = []
  while stk:
    u, p, d = stk.pop()
    res.append(d)
    for v in G[u]:
      if not used[v] and v != p:
        stk.append((v, u, d + S[v]))
  return res
        
stk = [0]
ans = 0
while stk:
  u = centroid(stk.pop())
  ds = []
  val = 0
  if S[u] == 1: ans += 1
  for v in G[u]:
    if used[v]: continue
    stk.append(v)
    d = totals(v, u)
    ans += sum(x + S[u] > 0 for x in d)
    d.sort()
    # d[i] + d[j] + S[u] > 0
    val -= sum(len(d) - bisect_left(d, -x - S[u] + 1) for x in d)
    ds.extend(d)
  ds.sort()
  val += sum(len(ds) - bisect_left(ds, -x - S[u] + 1) for x in ds)
  ans += val // 2
  used[u] = True
  
print(ans)