/in/foo.cc: In function 'int dfs(int, int, int)':
/in/foo.cc:28:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:107:29: warning: 'chengshi' may be used uninitialized in this function [-Wmaybe-uninitialized]
         cout << chengshi << " " << res << endl;
                             ^~~