import sys

sys.setrecursionlimit(200000)

n, u, v = map(int, input().split())

# nodeの値を-1しておく
u = u-1
v = v-1

# Making Adjacency list
Adj_dict = {}
for i in range(n):
    new = {i: []}
    Adj_dict.update(new)

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

def tree_distance(Adj_dict, start, Visited, distance, Dist_list):
    
    # 現在いる位置を Visited = True に変更する
    Visited[start] = True

    # 該当するnodeの距離を記録して、distanceを1加算する
    Dist_list[start] = distance
    distance += 1

    # 訪れていないnodeに対して、dfs
    for node in Adj_dict[start]:
        if Visited[node] == False:
            tree_distance(Adj_dict, node, Visited, distance, Dist_list)
    
    return


Dist_list = [0 for _ in range(n)]
Visited = [False for _ in range(n)]
distance = 0
tree_distance(Adj_dict, u, Visited, distance, Dist_list)
Taka = Dist_list

Dist_list = [0 for _ in range(n)]
Visited = [False for _ in range(n)]
distance = 0
tree_distance(Adj_dict, v, Visited, distance, Dist_list)
Aoki = Dist_list

Taka_num = 0
node = 0
for i in range(n):
    if Aoki[i] >= Taka[i]:
        if Taka[i] >= Taka_num:
            Taka_num = Taka[i]
            node = i

# TakahashiはTaka_numのnodeへ逃げる
ans = Aoki[node] -1

print(ans)