func_code_string: #include <bits/stdc++.h>   using namespace std;   const int Imx = 2147483647;   const long long Lbig = 2e18;   const int mod = 1e9 + 7;   struct fastio {     char s[100000];     int it, len;     fastio() { it = len = 0; }     inline char get() {       if (it < len) return s[it++];       it = 0;       len = fread(s, 1, 100000, stdin);       if (len == 0)         return EOF;       else         return s[it++];     }     bool notend() {       char c = get();       while (c ==     || c ==   n ) c = get();       if (it > 0) it--;       return c != EOF;     }   } _buff;   inline long long getnum() {     long long r = 0;     bool ng = 0;     char c;     c = _buff.get();     while (c !=  -  && (c <  0  || c >  9 )) c = _buff.get();     if (c ==  - ) ng = 1, c = _buff.get();     while (c >=  0  && c <=  9 ) r = r * 10 + c -  0 , c = _buff.get();     return ng ? -r : r;   }   template <class T>   inline void putnum(T x) {     if (x < 0) putchar( - ), x = -x;     register short a[20] = {}, sz = 0;     while (x) a[sz++] = x % 10, x /= 10;     if (sz == 0) putchar( 0 );     for (int i = sz - 1; i >= 0; i--) putchar( 0  + a[i]);   }   inline char getreal() {     char c = _buff.get();     while (c ==     || c ==   n ) c = _buff.get();     return c;   }   int n;   int head[500111], nxt[1000111], to[1000111], tot = 1;   int head2[500111], nxt2[1000111], to2[1000111], tot2 = 1;   int f[500111];   bool oc[500111], oc2[500111];   void adde(int x, int y) {     nxt[++tot] = head[x];     head[x] = tot;     to[tot] = y;   }   void adde2(int x, int y) {     nxt2[++tot2] = head2[x];     head2[x] = tot2;     to2[tot2] = y;   }   int gf(int x) { return f[x] == x ? x : f[x] = gf(f[x]); }   map<pair<int, int>, int> mpid;   int nid[500111];   void dfs(int x, int p = -1) {     for (int i = head[x]; i; i = nxt[i]) {       int u = to[i];       if (u == p) continue;       dfs(u, x);       if (oc[i >> 1]) continue;       int tmp = nid[gf(u)];       if (!tmp) continue;       putnum(u), putchar(   ), putnum(x), putchar(   );       putnum(to2[tmp]), putchar(   ), putnum(to2[tmp ^ 1]), putchar(  n );     }   }   void dfs2(int x, int p = -1) {     for (int i = head2[x]; i; i = nxt2[i]) {       int u = to2[i];       if (u == p) continue;       if (!oc2[i >> 1]) nid[gf(u)] = i;       dfs2(u, x);     }   }   int main() {     n = getnum();     for (int i = 1; i <= n; i++) f[i] = i;     for (int i = 1; i < n; i++) {       int x, y;       x = getnum(), y = getnum();       if (x > y) swap(x, y);       mpid[make_pair(x, y)] = i;       adde(x, y);       adde(y, x);     }     int cnt = n - 1;     for (int i = 1; i < n; i++) {       int x, y;       x = getnum(), y = getnum();       if (x > y) swap(x, y);       if (mpid.find(make_pair(x, y)) != mpid.end()) {         oc[mpid[make_pair(x, y)]] = 1;         oc2[i] = 1;         cnt--;         f[gf(x)] = gf(y);       }       adde2(x, y);       adde2(y, x);     }     dfs2(1);     putnum(cnt), putchar(  n );     dfs(1);     return 0;   }   