/in/foo.cc: In member function 'void graph::dfs2(int)':
/in/foo.cc:83:34: error: no matching function for call to 'graph::dfs2(int&, int&)'
                 top[v]=v,dfs2(v,v);
                                  ^
/in/foo.cc:75:10: note: candidate: void graph::dfs2(int)
     void dfs2(int u){
          ^~~~
/in/foo.cc:75:10: note:   candidate expects 1 argument, 2 provided