#include <bits/stdc++.h>

#include <unistd.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
 
 
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(25)<< fixed<<p<<endl;
int dx_ori[4] = { -1,0, 1,0 }, dy_ori[4] = { 0,1,0,-1 };
int dx[4] = {0, 0, 0, 0}, dy[4] = {0, 0, 0, 0};
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
const ll MOD = 1000000007;
//const ll MOD = 998244353;
// #define mp make_pair
//#define endl '\n'


class HLD {
private:
  void dfs_sz(int v) {
    for(int &u:G[v])
      if(u==par[v]) swap(u,G[v].back());
    if(~par[v]) G[v].pop_back();

    for(int &u:G[v]){
      par[u]=v;
      dep[u]=dep[v]+1;
      dfs_sz(u);
      sub[v]+=sub[u];
      if(sub[u]>sub[G[v][0]]) swap(u,G[v][0]);
    }
  }

  void dfs_hld(int v,int c,int &pos) {
    vid[v]=pos++;
    inv[vid[v]]=v;
    type[v]=c;
    for(int u:G[v]){
      if(u==par[v]) continue;
      head[u]=(u==G[v][0]?head[v]:u);
      dfs_hld(u,c,pos);
    }
  }

public:
  vector< vector<int> > G;
  vector<int> vid, head, sub, par, dep, inv, type;

  HLD(int n):
    G(n),vid(n,-1),head(n),sub(n,1),
    par(n,-1),dep(n,0),inv(n),type(n){}

  void add_edge(int u,int v) {
    G[u].emplace_back(v);
    G[v].emplace_back(u);
  }

  void build(vector<int> rs={0}) {
    int c=0,pos=0;
    for(int r:rs){
      dfs_sz(r);
      head[r]=r;
      dfs_hld(r,c++,pos);
    }
  }

  int lca(int u,int v){
    while(1){
      if(vid[u]>vid[v]) swap(u,v);
      if(head[u]==head[v]) return u;
      v=par[head[v]];
    }
  }

  int distance(int u,int v){
    return dep[u]+dep[v]-2*dep[lca(u,v)];
  }

  // for_each(vertex)
  // [l, r) <- attention!!
  template<typename F>
  void for_each(int u, int v, const F& f) {
    while(1){
      if(vid[u]>vid[v]) swap(u,v);
      f(max(vid[head[v]],vid[u]),vid[v]+1);
      if(head[u]!=head[v]) v=par[head[v]];
      else break;
    }
  }

  template<typename T,typename Q,typename F>
  T for_each(int u,int v,T ti,const Q &q,const F &f){
    T l=ti,r=ti;
    while(1){
      if(vid[u]>vid[v]){
        swap(u,v);
        swap(l,r);
      }
      l=f(l,q(max(vid[head[v]],vid[u]),vid[v]+1));
      if(head[u]!=head[v]) v=par[head[v]];
      else break;
    }
    return f(l,r);
  }

  // for_each(edge)
  // [l, r) <- attention!!
  template<typename F>
  void for_each_edge(int u, int v,const F& f) {
    while(1){
      if(vid[u]>vid[v]) swap(u,v);
      if(head[u]!=head[v]){
        f(vid[head[v]],vid[v]+1);
        v=par[head[v]];
      }else{
        if(u!=v) {
          f(vid[u]+1,vid[v]+1);
        }
        break;
      }
    }
  }
};


vi depth(100001);
vii G(100001);

void dfs(int now, int par, int dept) {
  depth[now] = dept;
  rep (i, G[now].size()) {
    int ch = G[now][i];
    if (ch == par) continue;
    dfs(ch, now, dept + 1);
  }
}

signed main() {
  int n, u, v;
  cin >> n >> u >> v;
  u--; v--;
  depth.resize(n);
  HLD hld(n);
  rep (i, n - 1) {
    int u, v;
    cin >> u >> v;
    u--; v--;
    G[u].push_back(v);
    G[v].push_back(u);
    hld.add_edge(u, v);
  }
  hld.build(vi(1, v));

  dfs(v, -1, 0);

  //DEBUG_VEC(depth);

  priority_queue<pii> pq;
  rep (i, n) {
    pq.push(pii(depth[i], i));
  }

  int res = 0;
  while (pq.size() > 0) {
    pii temp = pq.top();
    pq.pop();
    //DEBUG(temp);
    int ans = temp.first, s = temp.second;

    int lc = hld.lca(s, u);
    if (depth[lc] > depth[u] - depth[lc]) {
      if (depth[u] % 2 == 1) {
        chmax(res, ans - 1);
      }
      else {
        chmax(res, ans - 1);
      }
    }
  }
  cout << res << endl;
}


Measured memory_bytes: 23796