#include <bits/stdc++.h>
using namespace std;
template <typename T>
using pq = priority_queue<T, vector<T>, greater<T>>;
using ll = long long;
ll INF = LLONG_MAX / 10 - 100;
ll mod = 1e9 + 7;
long long dx[] = {-1, 0, 1, 0}, dy[] = {0, 1, 0, -1};
vector<ll> prime;
double pi = 3.141592653689793238;
class fact {
 public:
  long long fmod = 1e9 + 7;
  vector<long long> fac, finv, inv;
  fact(long long n, long long Mod = 1e9 + 7) {
    fmod = Mod;
    fac = vector<long long>(n + 1, 0);
    finv = vector<long long>(n + 1, 0);
    inv = vector<long long>(n + 1, 0);
    fac[0] = 1;
    for (long long i = 1; i < n + 1; i++) fac[i] = fac[i - 1] * i % fmod;
    for (long long i = 0; i < n + 1; i++) finv[i] = fact::POW(fac[i], fmod - 2);
    for (long long i = 0; i < n + 1; i++) inv[i] = POW(i, fmod - 2);
  }
  ll nCr(ll n, ll r) {
    if (n < r) return 0;
    return (fac[n] * finv[r] % fmod) * finv[n - r] % fmod;
  }
  ll POW(ll a, ll b) {
    ll c = 1;
    while (b > 0) {
      if (b & 1) {
        c = a * c % fmod;
      }
      a = a * a % fmod;
      b >>= 1;
    }
    return c;
  }
  inline long long operator[](long long i) { return fac[i]; }
};
void DEBUG(vector<long long> a) {
  for (long long i = 0; i < a.size(); i++) cout << a[i] << " ";
  cout << endl;
}
void EMP(long long x) { cout << "!!!" << x << "!!!" << endl; }
ll GCD(ll a, ll b) {
  ll c;
  while (b != 0) {
    c = a % b;
    a = b;
    b = c;
  }
  return a;
}
ll LCM(ll a, ll b) { return (a / GCD(a, b)) * (b / GCD(a, b)) * GCD(a, b); }
ll POW(ll a, ll b) {
  ll c = 1;
  while (b > 0) {
    if (b & 1) {
      c = a * c % mod;
    }
    a = a * a % mod;
    b >>= 1;
  }
  return c;
}
void PRI(ll n) {
  bool a[n + 1LL];
  for (long long i = 0; i < n + 1LL; i++) {
    a[i] = 1LL;
  }
  for (long long i = 2; i < n + 1LL; i++) {
    if (a[i]) {
      prime.push_back(i);
      ll b = i;
      while (b <= n) {
        a[b] = 0;
        b += i;
      }
    }
  }
}
template <typename T>
T chmin(T& a, T b) {
  if (a > b) a = b;
  return a;
}
template <typename T>
T chmax(T& a, T b) {
  if (a < b) a = b;
  return b;
}
bool isSqrt(ll a) { return pow(sqrt(a), 2) == a ? 1 : 0; }
void YesNo(bool a) {
  if (a)
    cout << "Yes";
  else
    cout << "No";
  cout << endl;
}
void yesno(bool a) {
  if (a)
    cout << "yes";
  else
    cout << "no";
  cout << endl;
}
void YESNO(bool a) {
  if (a)
    cout << "YES";
  else
    cout << "NO";
  cout << endl;
}
double dis(long long x1, long long x2, long long y1, long long y2) {
  return sqrt((double)abs(x1 - x2) * (double)abs(x1 - x2) +
              (double)abs(y1 - y2) * (double)abs(y1 - y2));
}
long long ceili(long long x, long long y) {
  if (x % y == 0)
    return x / y;
  else
    return x / y + 1;
}
long long extGCD(long long a, long long b, long long& x, long long& y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}
class UnionFind {
 private:
  vector<long long> par;

 public:
  UnionFind(long long N) { par = vector<long long>(N, -1); }
  long long find(long long x);
  ll size(long long x);
  void unite(long long x, long long y);
  bool same(long long x, long long y);
};
long long UnionFind::find(long long x) {
  if (par[x] < 0)
    return x;
  else
    return par[x] = find(par[x]);
}
ll UnionFind::size(long long x) { return -par[find(x)]; }
void UnionFind::unite(long long x, long long y) {
  x = find(x);
  y = find(y);
  if (x == y) return;
  if (size(x) < size(y)) swap(x, y);
  par[x] += par[y];
  par[y] = x;
}
bool UnionFind::same(long long x, long long y) {
  x = find(x);
  y = find(y);
  return x == y;
}
inline unsigned mul(unsigned a, unsigned b, unsigned mod = 1000000007) {
  unsigned long long x = (unsigned long long)a * b;
  unsigned xh = (unsigned)(x >> 32), xl = (unsigned)x, d, m;
  asm("divl %4; \n\t" : "=a"(d), "=d"(m) : "d"(xh), "a"(xl), "r"(mod));
  return m;
}
vector<long long> g[100005];
vector<long long> dist(100005, 0);
vector<bool> visited(100005, false);
vector<long long> distA(100005, INF), distB(100005, INF);
long long dfs(long long u) {
  for (auto to : g[u]) {
    if (visited[to]) continue;
    if (distA[to] >= distB[to]) continue;
    chmax(dist[u], dfs(to) + 1);
  }
}
void solve() {
  long long n, u, v;
  cin >> n >> u >> v;
  --u, --v;
  for (long long(i) = (0); (i) < (n - 1); (i)++) {
    long long a, b;
    cin >> a >> b;
    --a, --b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  distA[u] = 0;
  distB[v] = 0;
  queue<long long> q;
  q.push(u);
  while (q.size()) {
    long long nxt = q.front();
    q.pop();
    for (auto to : g[nxt]) {
      if (distA[to] > distA[nxt] + 1) {
        distA[to] = distA[nxt] + 1;
        q.push(to);
      }
    }
  }
  q = queue<long long>();
  q.push(v);
  while (q.size()) {
    long long nxt = q.front();
    q.pop();
    for (auto to : g[nxt]) {
      if (distB[to] > distB[nxt] + 1) {
        distB[to] = distB[nxt] + 1;
        q.push(to);
      }
    }
  }
  bool odd = distA[v] % 2;
  long long ans = 0;
  for (long long(i) = (0); (i) < (n); (i)++) {
    if (distA[i] >= distB[i]) continue;
    if ((distB[i] - distA[i]) % 2 == 1) {
      chmax(ans, distB[i] - 1);
    } else {
      chmax(ans, distB[i]);
    }
  }
  cout << ans << endl;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
}
