SP6818 CAPCITY - Capital City
Description
There are N cities in Flatland connected with M unidirectional roads. The cities are numbered from 1 to N. The Flat Circle of Flatland (FCF) wants to set up a new capital city for his kingdom. For security reasons, _the capital must be reachable from all other cities_ of Flatland. FCF needs the list of _all_ candidate cities. You are the chief programmer at FACM (Flat Association for Computing Machinery) responsible for providing the list to FCF as soon as possible.
**Input**
The first line of the input file contains two integers։ 1N and 1M. Each of the following M lines contains two integers 1A, B
**Output**
The output file contains an integer denoting the number of candidate cities followed by the list of candidate cities in increasing order.
**Example**
Input:
4 4
1 2
3 2
4 3
2 1
Output:
2
1 2
Input Format
N/A
Output Format
N/A