#include <bits/stdc++.h>
using namespace std;
#define e1 first
#define e2 second
#define pb push_back
#define mp make_pair
#define boost ios_base::sync_with_stdio(false)
#define eb emplace_back
#define OUT(x) {cout << x; exit(0); }
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define scanf(...) scanf(__VA_ARGS__)?:0
typedef long long int ll;
typedef unsigned long long ull;
typedef pair <int, int> PII;
typedef pair <ll, ll> PLL;
typedef pair <PLL, int> PLLI;
typedef pair <PLL, PLL> PP;
typedef pair <PII, int> PPI;
typedef pair <ll, int> PLI;
typedef unsigned int ui;
const int inf = 1e9+9;
const ll MOD = 1e9+696969;
const long long INF = 1e18+3;
#define maxn 1001000
vector <int> v[maxn];
int parent[maxn], n, root, goal, a ,b, d[maxn];
bool onpath[maxn];
int POST[maxn], VER;
void countEverything(int x, int par)
{
    parent[x] = par;
    for (auto u : v[x])
        if (u != par)
        {
            d[u] = d[x] + 1;
            countEverything(u, x);
        }
    POST[++VER] = x;
}

int cost[maxn];
inline int deg(int x) {
    return (int)v[x].size();
}
int sciezka[maxn], DS;

void dfs(int x, int par) {
    //cout << "Where am i: " << x << endl;
    for (auto u : v[x])
        if (!onpath[u] && u != par)
        {
            cost[u] = cost[x] + deg(u) - 1;
            dfs(u, x);
        }
}
bool zle[maxn];
int dp[maxn];
bool check(int k)
{
    FOR(i, 1, n) dp[i] = 0;
    FOR(i, 1, n)
    {
        int x = POST[i];
        dp[x]--;
        if (cost[x] > k) dp[x] = 1;
        else dp[x] = max(0, dp[x]);
        dp[x] = min(dp[x], 1);
        if (x != root) dp[parent[x]] += dp[x];
    }
    return (dp[root] == 0);
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    cin >> n >> goal >> root;
    assert(goal <= n); assert(root <= n);
    if (goal == root) OUT(0);
    FOR(i, 2, n)
    {
        cin >> a >> b;
        v[a].pb(b);
        v[b].pb(a);
    }
    countEverything(root, root);
    int x = goal, y = 0;
    while (x != root)
    {
        onpath[x] = 1;
        sciezka[++DS] = x;
        x = parent[x];
    }
    onpath[root] = 1;
    sciezka[++DS] = x;
    int pathOnly = 0;

    pathOnly -= (d[goal] - 1);
    FOR(i, 1, DS)
    {
        int u = sciezka[i];
        if (u != goal) pathOnly += deg(sciezka[i]) - 1;
        if (u != goal) dfs(u, u);
    }

    x = 0, y = n + n;
    while (x < y)
    {
        int sr = (x + y) >> 1;
        if (!check(sr)) x = ++sr;
        else y = sr;
    }

    cout << pathOnly + x;
}