You have to complete $n$ courses. There are $m$ requirements of the form "course $a$ has to be completed before course $b$ ". Your task is to find an order in which you can complete the courses.
The first input line has two integers $n$ and $m$ : the number of courses and requirements. The courses are numbered $1,2,\dots,n$ .
After this, there are $m$ lines describing the requirements. Each line has two integers $a$ and $b$ : course $a$ has to be completed before course $b$ .
Print an order in which you can complete the courses. You can print any valid order that includes all the courses.
If there are no solutions, print IMPOSSIBLE.