#include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     int n, x;     cin >> n >> x;     vector<int> v[n + 1];     for (int i = 0; i < n - 1; i++) {       int a, b;       cin >> a >> b;       v[a].push_back(b);       v[b].push_back(a);     }     bool vstd[n + 1];     int dst1[n + 1];     int dst2[n + 1];     memset(vstd, false, sizeof vstd);     memset(dst1, 0x7f, sizeof dst1);     memset(dst2, 0x7f, sizeof dst2);     queue<int> q;     q.push(1);     dst1[1] = 0;     while (q.size()) {       int node = q.front();       q.pop();       if (vstd[node]) continue;       vstd[node] = true;       for (auto u : v[node]) {         dst1[u] = min(dst1[u], dst1[node] + 1);         q.push(u);       }     }     q.push(x);     dst2[x] = 0;     memset(vstd, false, sizeof vstd);     while (q.size()) {       int node = q.front();       q.pop();       if (vstd[node]) continue;       vstd[node] = true;       for (auto u : v[node]) {         dst2[u] = min(dst2[u], dst2[node] + 1);         q.push(u);       }     }     int ans = 0;     for (int i = 1; i <= n; i++) {       if (dst1[i] > dst2[i]) {         ans = max(ans, max(2 * dst1[i], 2 * dst2[i]));       }     }     cout << ans << endl;     return 0;   }   