/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:7:17: error: 'f' was not declared in this scope
    7 |         int num=f[u]+cnt;
      |                 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:27:17: error: 'f' was not declared in this scope
   27 |                 f[x]++;
      |                 ^