#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 1e6 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
vector<int> adj[N];
vector<int> dp(N);
void dfs1(int u, int p){
int deg = sz(adj[u])-(p != -1);
dp[u] = deg;
vector<int> vals;
vals.pb(0), vals.pb(0);
trav(v,adj[u]){
if(v == p) conts;
dfs1(v,u);
vals.pb(dp[v]);
}
sort(rall(vals));
dp[u] += vals[1];
}
vector<int> curr_path;
vector<int> path;
void dfs2(int u, int p, int des){
curr_path.pb(u);
if(u == des){
path = curr_path;
}
trav(v,adj[u]){
if(v == p) conts;
dfs2(v,u,des);
}
curr_path.pop_back();
}
void solve(int test_case)
{
int n,t,m; cin >> n >> t >> m;
rep1(i,n-1){
int u,v; cin >> u >> v;
adj[u].pb(v), adj[v].pb(u);
}
dfs1(m,-1);
dfs2(m,-1,t);
path.pop_back();
vector<bool> on_path(n+5);
trav(u,path) on_path[u] = 1;
int ans = 0;
rep(i,sz(path)){
int u = path[i];
int deg = sz(adj[u])-(u != m)-1;
ans += deg;
}
auto ok = [&](int mid){
int moves = 0;
rep(i,sz(path)){
int u = path[i];
moves++;
vector<int> vals;
trav(v,adj[u]){
if(on_path[v]) conts;
vals.pb(dp[v]);
}
trav(x,vals){
if(x > mid){
moves--;
}
}
if(moves < 0) return false;
}
return true;
};
int l = 0, r = *max_element(all(dp));
int mn_add = -1;
while(l <= r){
int mid = (l+r) >> 1;
if(ok(mid)){
mn_add = mid;
r = mid-1;
}
else{
l = mid+1;
}
}
assert(mn_add != -1);
ans += mn_add;
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
