func_code_string: #include <bits/stdc++.h>   const int p = 1000000007;   int c[12][15], e[12][15], g[12][5000], h[12][5000];   int edge1[3000], next1[3000], first1[3000], deg1[3000], sum_edge1;   int edge2[30], next2[30], first2[30], deg2[30], sum_edge2;   int i, n1, n2, r, s, t, x, y;   inline int power(int x, int y) {     int s = 1;     for (int i = 30; i >= 0; i--) {       s = 1LL * s * s % p;       if (y & (1 << i)) s = 1LL * s * x % p;     }     return s;   }   inline void addedge1(int x, int y) {     sum_edge1++, edge1[sum_edge1] = y, next1[sum_edge1] = first1[x],                  first1[x] = sum_edge1, deg1[x]++;     return;   }   inline void addedge2(int x, int y) {     sum_edge2++, edge2[sum_edge2] = y, next2[sum_edge2] = first2[x],                  first2[x] = sum_edge2, deg2[x]++;     return;   }   inline int dfs1(int d, int x, int fx, int y, int fy) {     if (deg1[x] < deg2[y]) return 0;     int l = 0;     for (int j = 1; j <= n2; j++) e[d][j] = 0;     for (int j = first2[y]; j != 0; j = next2[j])       if (edge2[j] != fy) l++, e[d][edge2[j]] = l;     for (int i = 0; i < (1 << l); i++) g[d][i] = 0;     g[d][0] = 1;     for (int i = first1[x]; i != 0; i = next1[i])       if (edge1[i] != fx) {         for (int j = 0; j < (1 << l); j++) h[d][j] = g[d][j];         for (int j = first2[y]; j != 0; j = next2[j])           if (edge2[j] != fy)             c[d][e[d][edge2[j]]] = dfs1(d + 1, edge1[i], x, edge2[j], y);         for (int k = 1; k <= l; k++)           if (c[d][k])             for (int j = 0; j < (1 << l); j++)               if (!(j & (1 << (k - 1))))                 g[d][j | (1 << (k - 1))] =                     (g[d][j | (1 << (k - 1))] + 1LL * h[d][j] * c[d][k]) % p;       }     return g[d][(1 << l) - 1];   }   inline int dfs2(int d, int x, int fx, int y, int fy) {     if (deg2[x] < deg2[y]) return 0;     int l = 0;     for (int j = 1; j <= n2; j++) e[d][j] = 0;     for (int j = first2[y]; j != 0; j = next2[j])       if (edge2[j] != fy) l++, e[d][edge2[j]] = l;     for (int i = 0; i < (1 << l); i++) g[d][i] = 0;     g[d][0] = 1;     for (int i = first2[x]; i != 0; i = next2[i])       if (edge2[i] != fx) {         for (int j = 0; j < (1 << l); j++) h[d][j] = g[d][j];         for (int j = first2[y]; j != 0; j = next2[j])           if (edge2[j] != fy)             c[d][e[d][edge2[j]]] = dfs2(d + 1, edge2[i], x, edge2[j], y);         for (int k = 1; k <= l; k++)           if (c[d][k])             for (int j = 0; j < (1 << l); j++)               if (!(j & (1 << (k - 1))))                 g[d][j | (1 << (k - 1))] =                     (g[d][j | (1 << (k - 1))] + 1LL * h[d][j] * c[d][k]) % p;       }     return g[d][(1 << l) - 1];   }   inline void input() {     scanf( %d , &n1);     for (i = 1; i < n1; i++) {       scanf( %d%d , &x, &y);       addedge1(x, y), addedge1(y, x);     }     scanf( %d , &n2);     for (i = 1; i < n2; i++) {       scanf( %d%d , &x, &y);       addedge2(x, y), addedge2(y, x);     }     for (i = 1; i <= n2; i++)       if (deg2[i] > deg2[r]) r = i;     return;   }   int main() {     input();     for (i = 1; i <= n1; i++) s = (s + dfs1(0, i, 0, r, 0)) % p;     for (i = 1; i <= n2; i++) t = t + dfs2(0, i, 0, r, 0);     printf( %d , 1LL * s * power(t, p - 2) % p);     return 0;   }   