#include <bits/stdc++.h>

using namespace std;

#define rep(i, n) for(int i = 0; i < (n); ++i)
#define per(i, n) for(int i = (n)-1; i >= 0; --i)
#define eee(a) (cerr << (#a) << ": " << (a) << endl);
#define ppp(a) (cout << (a) << endl); 

using ll = long long;

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

constexpr int MOD = 1e9+7;
constexpr int INF = 1e9;
constexpr ll LINF = 1e18;
constexpr double phi = (1+sqrt(5))/2;
constexpr double pi = 3.14159265358979323846264338327950288;

ll gcd(ll a, ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b){return a/gcd(a,b)*b;}
inline void Yes(){puts("Yes");}
inline void No(){puts("No");}
inline void Judge(bool b){b?Yes():No();}
inline void YES(){puts("YES");}
inline void NO(){puts("NO");}
inline void JUDGE(bool b){b?YES():NO();}
inline ll powmod(ll b, ll e, ll mod){ll r=1;while(e>0){if(e&1)r=(r%mod)*(b%mod)%mod;b=(b%mod)*(b%mod)%mod;e>>=1;}return r;}
inline double distance(ll x1, ll y1, ll x2, ll y2){return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}
inline double d2r(double d){return d*pi/180;}
inline double r2d(double r){return r*180/pi;}

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 (b<a) { a=b; return 1; } return 0; }
template<typename T1, typename T2> ostream& operator<<(ostream& s, const pair<T1, T2>& p) {return s << "(" << p.first << ", " << p.second << ")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& v) {s<<'[';for(size_t i=0;i<v.size();++i){s<<v[i];if(i < v.size()-1)s<<", ";}s<<']';return s;}

vector<vector<int>> G;

vector<int> dis;
vector<int> aok;
void rec(int i, int p, int d, bool ao){
    dis[i] += d;
    if(ao) aok[i] += d;
    for(int ni : G[i]){
        if(p == ni) continue;
        rec(ni, i, d+1, ao);
    }
}

int main(){
    
    int n, u, v;
    scanf("%d%d%d", &n, &u, &v);
    G.resize(n);
    --u; --v;
    dis.resize(n, 0);
    aok.resize(n, 0);
    rep(i, n-1){
        int A, B;
        scanf("%d%d", &A, &B);
        --A; --B;
        G[A].emplace_back(B);
        G[B].emplace_back(A);
    }
    rec(u, -1, 0, false);
    rec(v, -1, 0, true);
    int en = max_element(dis.begin(), dis.end()) - dis.begin();
    ppp(aok[en]-1);
    return 0;
}
