Task Order Determination

You are given n tasks, numbered from 1 to n, and m dependency relations between them. Each dependency is given as a pair of integers (a, b) meaning that task a must be completed before task b. Your goal is to determine a valid order in which all tasks can be completed while satisfying all these dependencies.

If there is a cycle in the dependencies, then it is impossible to complete all tasks and you should output 0.

Formally, find an ordering of tasks such that for every dependency \(a \rightarrow b\), task a appears before task b in the ordering. If no valid ordering exists, output 0.

inputFormat

The input is read from stdin and has the following format:

n m
a1 b1
a2 b2
... 
am bm

Where:

• n is the number of tasks.
• m is the number of dependency pairs.
• Each of the next m lines contains two integers a and b indicating that task a must be done before task b.

outputFormat

The output is printed to stdout. If a valid task order exists, print the tasks in one valid order separated by a single space. If no valid order exists due to a cycle, print 0.

3 0

1 2 3