#include <bits/stdc++.h>
using namespace std;
const int N = (int) 1e6 + 7;
int n, tr, mo;
vector<int> g[N];
int par[N], cost[N];
void build_tree(int a, int p = -1) {
{
vector<int> Kids;
for (auto &b : g[a]) {
if (b != p) {
Kids.push_back(b);
}
}
g[a] = Kids;
}
cost[a] += (int) g[a].size() - 1;
for (auto &b : g[a]) {
cost[b] += cost[a];
build_tree(b, a);
}
par[a] = p;
}
void dfs(int a) {
for (auto &b : g[a]) {
dfs(b);
}
if ((int) g[a].size() == 0) {
return;
}
if ((int) g[a].size() == 1) {
return;
}
assert((int) g[a].size() >= 2);
vector<int> Values;
for (auto &b : g[a]) {
Values.push_back(cost[b]);
}
sort(Values.rbegin(), Values.rend());
assert((int) Values.size() >= 2);
cost[a] = Values[1];
}
signed main() {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
/// freopen ("input.txt", "r", stdin);
cin >> n >> tr >> mo;
for (int i = 1; i < n; i++) {
int a, b;
cin >> a >> b;
g[a].push_back(b);
g[b].push_back(a);
}
build_tree(tr);
dfs(tr);
cout << cost[mo] << "\n";
}
