CAPCITY  Capital City
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: 1 ≤ N ≤ 100,000 and 1 ≤ M ≤ 200,000. Each of the following M lines contains two integers 1 ≤ A, B ≤ N denoting a road from A to 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
hide comments
karan_batra:
20170106 15:52:51
Weak test cases. No test case when there is no capital city. 

hamjosh1:
20161113 10:51:38
Use fast IO costed me TLE 

vivekkodu:
20160926 21:39:01
It is accepting solution even in case of disconnected graph. 

mvk944:
20160921 20:12:32
guys this can be easily done without graphs...


noob909:
20160704 10:12:49
4 5


rishabh16196:
20160602 19:53:36
Is there something in testcase 20? I am getting rte.


VISHAL ASHANK:
20160521 10:10:56
nice one... 

[Mayank Pratap]:
20160410 11:15:08
Spent a lot of time in this problem... Finally AC :) 

minhthai:
20160330 12:36:24
too...many...lines...of...code 

GAURAV CHANDEL:
20160223 14:31:41
Lovely Graph Problem.. 
Added by:  Narek Saribekyan 
Date:  20100620 
Time limit:  1s4s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: NODEJS OBJC PERL6 SQLITE VB.NET 
Resource:  Armenian TST 2010, Round 2 