func_code_string: #include <bits/stdc++.h>   #pragma comment(linker,  /stack:200000000 )   #pragma GCC optimize( Ofast )   #pragma target( sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native )   using namespace std;   const int inf = 0x3f3f3f3f;   inline long long read() {     register long long x = 0, f = 1;     register char c = getchar();     for (; !isdigit(c); c = getchar())       if (c ==  - ) f = -1;     for (; isdigit(c); c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);     return x * f;   }   void write(long long x) {     if (x < 0) x = -x, putchar( - );     if (x >= 10) write(x / 10);     putchar(x % 10 +  0 );   }   void writeln(long long x) {     write(x);     puts(  );   }   const int N = 505050;   struct Ans {     int a, b, c, d;   } ans[N];   int n, x, y, cnt, f[N], fa[2][N];   vector<int> e[2][N];   int get(int x) { return f[x] == x ? x : f[x] = get(f[x]); }   void dfs(int id, int x, int f) {     for (int i = 0; i < e[id][x].size(); i++)       if (e[id][x][i] != f) {         fa[id][e[id][x][i]] = x;         dfs(id, e[id][x][i], x);       }   }   void dfs2(int x) {     for (int i = 0; i < e[0][x].size(); i++)       if (e[0][x][i] != fa[0][x]) {         int u = e[0][x][i];         dfs2(u);         if (u != fa[1][x] && x != fa[1][u])           ans[++cnt] = (Ans){u, x, get(u), fa[1][get(u)]};       }   }   int main() {     scanf( %d , &n);     for (int id = 0; id < 2; id++)       for (int i = 1; i < n; i++) {         scanf( %d%d , &x, &y);         e[id][x].push_back(y);         e[id][y].push_back(x);       }     dfs(0, 1, 0);     dfs(1, 1, 0);     f[1] = 1;     for (int i = 2; i <= n; i++) {       int u = fa[1][i];       if (fa[0][i] == u || fa[0][u] == i)         f[i] = u;       else         f[i] = i;     }     dfs2(1);     printf( %d n , cnt);     for (int i = 1; i <= cnt; i++)       printf( %d %d %d %d n , ans[i].a, ans[i].b, ans[i].c, ans[i].d);   }   