#include <algorithm>
#include <iostream>
using namespace std;
const int N = 1000000;
int *ej[N], eo[N], dp[N], ii[N];
void append(int i, int j) {
int o = eo[i]++;
if (!o)
ej[i] = (int *) malloc(sizeof *ej[i]);
else if (!(o & o - 1))
ej[i] = (int *) realloc(ej[i], (o << 1) * sizeof *ej[i]);
ej[i][o] = j;
}
void detach(int i, int j) {
for (int o = 0; o < eo[i]; o++)
if (ej[i][o] == j) {
swap(ej[i][o], ej[i][--eo[i]]);
return;
}
}
bool dfs(int p, int i, int t) {
detach(i, p);
bool yes = i == t;
for (int o = 0; o < eo[i]; o++) {
int j = ej[i][o];
if (dfs(i, j, t))
yes = true, swap(ej[i][o], ej[i][0]);
}
return yes;
}
void dfs0(int i) {
for (int o = 0; o < eo[i]; o++)
dfs0(ej[i][o]);
sort(ej[i], ej[i] + eo[i], [] (int j0, int j1) { return dp[j0] > dp[j1]; });
dp[i] = eo[i];
for (int o = 1; o < eo[i]; o += 2)
dp[i] += dp[ej[i][o]];
}
int main() {
ios_base::sync_with_stdio(false), cin.tie(NULL);
int n, s, t; cin >> n >> t >> s, s--, t--;
for (int h = 0; h < n - 1; h++) {
int i, j; cin >> i >> j, i--, j--;
append(i, j), append(j, i);
}
dfs(-1, s, t);
int k = 0;
for (int i = s, j; i != t; i = j) {
j = ej[ii[k++] = i][0];
for (int o = 1; o < eo[i]; o++)
dfs0(ej[i][o - 1] = ej[i][o]);
sort(ej[i], ej[i] + --eo[i], [] (int j0, int j1) { return dp[j0] > dp[j1]; });
}
int ans = eo[ii[0]] + eo[ii[1]];
for (int o = 1; o < eo[ii[0]]; o += 2)
ans += dp[ej[ii[0]][o]];
for (int o = (eo[ii[0]] % 2 == 0) + 1; o < eo[ii[1]]; o += 2)
ans += dp[ej[ii[1]][o]];
cout << ans << '\n';
return 0;
}
