#include <bits/stdc++.h> // ver2.3.8
#include <boost/math/tools/minima.hpp>
#include <boost/multiprecision/cpp_int.hpp>
#define fmin brent_find_minima
#define int long long
#define endl "\n"
#define ALL(v) (v).begin(),(v).end()
#define COUNT(a,k) upper_bound(ALL(a),k)-lower_bound(ALL(a),k)
#define BIGGER(a,k) a.end()-upper_bound(ALL(a),k)
#define SMALLER(a,k) lower_bound(ALL(a),k)-a.begin()
#define Vi vector<int>
#define VVi vector<Vi>
#define Vs vector<string>
#define Pii pair<int,int>
#define VPii vector<Pii>
#define Tiii tuple<int,int,int>
#define VTiii vector<Tiii>
#define PQi priority_queue<int>
#define PQir priority_queue<int,vector<int>,greater<int>>
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define itos to_string
#define stoi stoll
#define FI first
#define SE second
#define cYES cout<<"YES"<<endl
#define cNO cout<<"NO"<<endl
#define cYes cout<<"Yes"<<endl
#define cNo cout<<"No"<<endl
#define cyes cout<<"yes"<<endl
#define cno cout<<"no"<<endl
#define sortr(v) sort(v,greater<>())
#define rep(i,a,b) for(int i=a;i<b;i++)
#define repeq(i,a,b) for(int i=a;i<=b;i++)
#define repreq(i,a,b) for(int i=a;i>=b;i--)
#define leng(n) (int)(log10(n)+1)
#define dem(a,b) ((a+b-1)/(b))
#define Vin(a) rep(iI,0,a.size())cin>>a[iI]
#define INF 3000000000000000000  //  3.0*10^18(MAXの1/3くらい)
#define MAX LLONG_MAX
#define PI 3.141592653589793238462
#define MOD 1000000007  //  10^9 + 7

using namespace std;
/* fmin(f,L,R,100) で関数の最小値を(x,min)で返す　*/
using boost::math::tools::brent_find_minima;
/* cpp_int (任意の長さのint) */
using boost::multiprecision::cpp_int;

/* デバッグ用 */
void Vout(auto a){if(a.size()==0) cout<<"."<<endl;
else{rep(i,0,a.size()-1)cout<<a[i]<<' ';if(a.size()>0)cout<<a.back()<<endl;}return;}
void Verr(auto a){if(a.size()==0) cerr<<"."<<endl;
else{rep(i,0,a.size()-1)cerr<<a[i]<<' ';if(a.size()>0)cerr<<a.back()<<endl;}return;}
void VVout(auto a){if(a.size()==0)cout<<"."<<endl;
else{rep(i,0,a.size())Vout(a[i]);}return;}
void VVerr(auto a){if(a.size()==0)cerr<<"."<<endl;
else{rep(i,0,a.size())Verr(a[i]);}return;}
void VPout(auto a){if(a.size()==0)cout<<"."<<endl;
else{rep(i,0,a.size())cout<<a[i].FI<<' '<<a[i].SE<<endl;}return;}
void VPerr(auto a){if(a.size()==0)cerr<<"."<<endl;
else{rep(i,0,a.size())cerr<<a[i].FI<<' '<<a[i].SE<<endl;}return;}

/* 便利関数 */
int gcd(int a,int b){return b?gcd(b,a%b):a;} // 最大公約数gcd
int lcm(int a,int b){return a/gcd(a,b)*b;} // 最小公倍数lcm
int mypow(int x, int n, int m){ // 累乗x^n(mod m) O(log(n))
if(n==0)return 1;if(n%2==0)return mypow(x*x%m,n/2,m);else return x*mypow(x,n-1,m)%m;}
int scomb(int n, int r){if((n-r)<r)r=n-r; // nCr(小さい場合)
int a=1;for(int i=n;i>n-r;--i){a=a*i;}for(int i=1;i<r+1;++i){a=a/i;}return a;}
int comb(int n, int r){if((n-r)<r)r=n-r; // nCr(%MOD)
int a=1;for(int i=n;i>n-r;--i){a=a*i%MOD;}for(int i=1;
i<r+1;++i){a=a*mypow(i,MOD-2,MOD)%MOD;}return a%MOD;}
Vi stpowV(){Vi a(100001);
a[0]=1;repeq(i,1,100000)a[i]=a[i-1]*i%MOD;return a;}
//Vi stpow = stpowV();  // 階乗配列(%MOD)
Vi Vsum(Vi &v){Vi S(v.size()+1);rep(i,1,S.size())S[i]+=v[i-1]+S[i-1];return S;}// 累積和
int digit(int k,int i){string s = itos(k);return s[s.size()-i]-'0';} // i桁目の数字
void press(auto &v){v.erase(unique(ALL(v)),v.end());} // 圧縮
Vi zip(Vi b){int Z=b.size(); // 座標圧縮
Pii p[Z+10];int a=b.size();Vi l(a);for(int i=0;i<a;i++)
p[i]=mp(b[i],i);sort(p,p+a);int w=0;for(int i=0;i<a;i++)
{if(i&&p[i].first!=p[i-1].first)w++;l[p[i].second]=w;}return l;}
Vi beki2V(){Vi a(61);int q = 1;rep(i,0,61){a[i]=q;q*=2;}return a;}
//Vi beki2 = beki2V(); // 2^n配列
int modiv(int a,int b){return a*mypow(b,MOD-2,MOD)%MOD;} // a÷b(MOD環境)

Vi par;
Vi dep;
VVi chi;

struct TreeAna {
  
  /* 使い方 */
  /*
  
  TreeAna tree(n) // 宣言 nは頂点数
  tree.connect(a,b) // 頂点aとbをつなぐ(0-index)
  tree.preset() // 頂点をつなぎ終わったら必ずこれをする！！！！！！！
  tree.make(k) // 頂点kを根としてpar,dep,chiを作り上げる
  tree.set_parII // lcaを使う前に必ずこれをする！！！！！！！
  tree.lca(a,b) // 頂点aとbの共通の"先祖"で一番近い"頂点"を返す
  
  */
  
  VVi parII;
  VPii memot;
  Vi treeFI;
  
  TreeAna(int n) {
    par = Vi(n);
    dep = Vi(n);
    chi = VVi(n);
  }
  
  void set_parII(){
    int n = par.size();
    parII = VVi(n,Vi(20,-1));
    rep(i,0,n) parII[i][0] = par[i];
    rep(i,0,19){
      rep(j,0,n){
        if(parII[j][i] == -1) parII[j][i+1] = -1;
        else parII[j][i+1] = parII[parII[j][i]][i];
      }
    }
    return;
  }
  
  int lca(int u,int v) { // 頂点uと頂点vの共通の"先祖"で一番近いやつを返す
    if(dep[u] > dep[v]) swap(u,v);
    
    for(int i=19;i>=0;i--) {
      if(((dep[v]-dep[u])>>i)&1) v = parII[v][i];
    }
    if(u==v) return u;
    for(int i=19;i>=0;i--) {
      if(parII[u][i] != parII[v][i]){
        u = parII[u][i];
        v = parII[v][i];
      }
    }
    return parII[u][0];
  }
  
  void connect(int a,int b) {
    memot.pb(mp(a,b));
    memot.pb(mp(b,a));
    return;
  }
  
  void preset() {
    sort(ALL(memot));
    rep(i,0,memot.size()) treeFI.pb(memot[i].FI);
    return;
  }
  
  void make(int root) {
    int st,en,now;
    int n = par.size();
    par = Vi(n,-2);
    dep = par;
    chi = VVi(n,Vi(0));
    par[root] = -1;
    dep[root] = 0;
    queue<int> next;
    next.push(root);
    while(!next.empty()){
      now = next.front();
      next.pop();
      st = lower_bound(ALL(treeFI), now)-treeFI.begin();
      en = upper_bound(ALL(treeFI), now)-treeFI.begin();
      rep(i,st,en){
        if(par[memot[i].SE]!=-2) continue;
        next.push(memot[i].SE);
        chi[now].pb(memot[i].SE);
        par[memot[i].SE] = now;
        dep[memot[i].SE] = dep[now]+1;
      }
    }
  }
};



signed main() {
  cin.tie(0);cout.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(12);
  /* 使い方 */
  /*
  
  TreeAna tree(n) // 宣言 nは頂点数
  tree.connect(a,b) // 頂点aとbをつなぐ(0-index)
  tree.preset() // 頂点をつなぎ終わったら必ずこれをする！！！！！！！
  tree.make(k) // 頂点kを根としてpar,dep,chiを作り上げる
  tree.set_parII() // lcaを使う前に必ずこれをする！！！！！！！
  tree.lca(a,b) // 頂点aとbの共通の"先祖"で一番近い"頂点"を返す
  
  */
  int n,T,A;
  cin >> n >> T >> A;
  T--,A--;
  TreeAna tree(n);
  int qw,er;
  rep(i,0,n-1){
    cin >> qw >> er;
    qw--,er--;
    tree.connect(qw,er);
  }
  tree.preset();
  tree.make(A);
  
  Vi chinasi(0);
  rep(i,0,n){
    if(chi[i].size()==0) chinasi.pb(i);
  }
  
  
  Vi sita(n,-1);
  
  rep(i,0,chinasi.size()){
    int now = chinasi[i];
    int ct = 0;
    while(1){
      if(sita[now] >= ct) break;
      else {
        sita[now] = ct;
        ct++;
        now = par[now];
        if(par[now] == -1) break;
      }
    }
  }
  
  //Verr(sita);
  int guuki = dep[T]%2;
  int d = dep[T];
  int can = (d-1)/2;
  
  int maxx = sita[T];
  int nowd = T;
  int maxd = T;
  
  rep(i,0,can){
    nowd = par[nowd];
    if(maxx < sita[nowd]){
      maxx = sita[nowd];
      maxd = nowd;
    }
  }
  
  int hukasa = dep[maxd] + maxx;
  
  if(1){
    cout << hukasa-1 << endl;
  }
  //else cout << hukasa << endl;
  
  
  
  return 0;
}


Measured memory_bytes: 12724