func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long MOD = pow(10, 9) + 7;   long long fac[1001];   template <typename T, typename U>   static inline void amin(T &x, U y) {     if (y < x) x = y;   }   template <typename T, typename U>   static inline void amax(T &x, U y) {     if (x < y) x = y;   }   void SieveOfEratosthenes(long long n) {     bool prime[n + 1];     memset(prime, true, sizeof(prime));     for (long long p = 2; p * p <= n; p++) {       if (prime[p] == true) {         for (long long i = p * p; i <= n; i += p) prime[i] = false;       }     }     for (long long p = 2; p <= n; p++)       if (prime[p])         ;   }   long long power(long long x, long long y, long long p) {     long long res = 1;     x = x % p;     while (y > 0) {       if (y & 1) res = (res * x) % p;       y = y >> 1;       x = (x * x) % p;     }     return res;   }   long long modInverse(long long n, long long p) { return power(n, p - 2, p); }   long long nCrModPFermat(long long n, long long r, long long p) {     if (n < r) return 0;     if (r == 0) return 1;     return (fac[n] * modInverse(fac[r], p) % p * modInverse(fac[n - r], p) % p) %            p;   }   void dfs(long long v, vector<vector<long long>> &adj, vector<long long> &used,            vector<long long> &maxD) {     for (long long u : adj[v]) {       if (!used[u]) {         used[u] = 1;         if (adj[u].size() == 1 && u != 1) {           maxD[u] = 0;           amax(maxD[v], 1 + maxD[u]);         } else {           dfs(u, adj, used, maxD);           amax(maxD[v], 1 + maxD[u]);         }       }     }   }   void solve() {     long long n, x, i;     cin >> n >> x;     vector<vector<long long>> adj(n + 1);     long long u, v;     for (i = 2; i <= n; i++) {       cin >> u >> v;       adj[u].push_back(v);       adj[v].push_back(u);     }     vector<long long> d(n + 1);     d[1] = 0;     vector<long long> visited(n + 1);     vector<long long> parent(n + 1);     visited[1] = 1;     parent[1] = 0;     queue<long long> q;     q.push(1);     while (!q.empty()) {       long long p = q.front();       q.pop();       for (auto el : adj[p]) {         if (!visited[el]) {           visited[el] = 1;           q.push(el);           d[el] = d[p] + 1;           parent[el] = p;         }       }     }     vector<long long> maxD(n + 1), used(n + 1);     used[1] = 1;     dfs(1, adj, used, maxD);     long long f = 1, ans = max(maxD[x] * 2, (abs(d[1] - d[x]) + maxD[x]) * 2),               start = x;     while (f) {       long long el = parent[x];       if (abs(d[el] - d[1]) > abs(d[el] - d[start])) {         long long z = max(maxD[el] * 2, (abs(d[1] - d[el]) + maxD[el]) * 2);         amax(ans, z);         x = el;       } else {         f = 0;         break;       }     }     cout << ans << endl;     return;   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     long long test = 1;     switch (test) {       case 1:         solve();         break;       case 2: {         long long t;         cin >> t;         while (t--) {           solve();         }       }; break;     }   }   