import sys
n,u,v=map(int,input().split())
l=[list(map(int,input().split())) for i in range(n-1)]
connection=[[] for i in range(n)]
for i in range(n-1):
  connection[l[i][0]-1].append(l[i][1]-1)
  connection[l[i][1]-1].append(l[i][0]-1)

def bfs(v):
  distance=[-1]*n
  distance[v]=0
  next=connection[v]
  next2=set()
  visited=[-1]*n
  visited[v]=1
  visitct=1
  ct=0
  while len(next)!=0 and visitct!=n:
    ct+=1
    for i in range(len(next)):
      if visited[next[i]]==-1:
        distance[next[i]]=ct
        visited[next[i]]=1
        visitct+=1
        for j in range(len(connection[next[i]])):
          if visited[connection[next[i]][j]]==-1:
            next2.add(connection[next[i]][j])
    next=list(next2)
    next2=set()
  return distance

x=bfs(u-1)
y=bfs(v-1)
ans=[]
e=[]
ct0=0
for i in range(n):
  if x[i]<y[i] and x[i]!=0:
    ct0+=1
if ct0==0:
  if x[v-1]==1:
    print(0)
  else:
    print(1)
  sys.exit()
for i in range(n):
  if x[i]<y[i]:
    if abs(x[i]-y[i])%2==0:
      if x[i]%2==1:
        ans.append(y[i]-1)
      else:
        ans.append(y[i]-2)
    else:
      ans.append(y[i]-1)
print(max(ans))