## Problem B. Topological sorting ≡

 Author: StdAlg Time limit: 1 sec Input file: input.txt Memory limit: 8 Mb Output file: output.txt

### Statement

You are to write a program that performs a topological sorting of a directed graph. Graph contains N vertices, numbered with integers from 1 to N, and M edges.

In other words, given a partial order on numbers from 1 to N, your program must produce some linear order on these numbers which does not conflict with the given partial order.

### Input file format

Input file contains two integers N and M, followed by M pairs of integers. Integers in each pair are different, and represent starting and ending vertex of a graph edge.

These pairs may also be considered comparisons where the first number precedes the second one.

### Output file format

Output file must contain a permutation of integers from 1 to N — numbers of vertices sorted in topological order. (That is, representing a linear order.) If ordering is not possible, output file must contain a single number 1.

### Constraints

0 ≤ N, M ≤ 100000

### Sample tests

No. Input file (input.txt) Output file (output.txt)
1
4 3
1 2
1 3
3 4
1 3 2 4

0.083s 0.011s 13