sys.setrecursionlimit(100000)

class Tree:
  C, RL = {}, {}
  R, N, D, S, P = None, None, None, None, None
  def __init__(s, num):
    s.N = num
  def setC(s, a, b):
    if a in s.C: s.C[a].append(b)
    else: s.C[a] = [b]
    if b in s.C: s.C[b].append(a)
    else: s.C[b] = [a]
  def makeRank(s, root):
    s.R = [0] * s.N
    s.R[root] = 1
    s.RL[1] = [root]
    s.S = {}
    s.P = {}
    F = [root]
    s.D = 2
    while F != []:
      Ft = []
      s.RL[s.D] = []
      for i in F:
        for j in s.C[i]:
          if s.R[j] == 0:
            s.R[j] = s.D
            Ft.append(j)
            s.RL[s.D].append(j)
            if i not in s.S:
              s.S[i] = [j]
            else:
              s.S[i].append(j)
            s.P[j] = i

      s.D += 1
      F = Ft
  def getDeep(s, x):
    ans = 0
    if x in s.S:
      for i in s.S[x]:
        ans = max(ans, s.getDeep(i))
      return ans + 1
    else:
      return 0
  def getParent(s, x, n):
    if n == 0:
      return x
    return s.getParent(s.P[x], n - 1)
    

N, u, v = list(map(int, input().split()))
AB = [list(map(int, input().split())) for _ in range(N - 1)]

T = Tree(N)
for a, b in AB:
  T.setC(a - 1, b - 1)

T.makeRank(v - 1)
t = (T.R[u - 1] // 2) - 1
f = T.R[u - 1] % 2
k = T.getDeep(T.getParent(u - 1, t))
print(t + k + f)

