View Compilation Error

0_0_27395756_9075.cpp: In function 'int main()':
0_0_27395756_9075.cpp:47:32: error: invalid initialization of non-const reference of type 'int&' from an rvalue of type 'int'
   for(int i=1;i<=n;i++) dfs(i,0);
                                ^
0_0_27395756_9075.cpp:15:6: note: in passing argument 2 of 'void dfs(int, int&)'
 void dfs(int u,int &f)
      ^