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
ashishgup:
20180918 22:44:31
20th test case for me was not printing the cities in increasing order :( 

preet_t:
20180829 08:09:23
can also be solved using Kosaraju's algo. 

m__sharma:
20180814 09:58:49
TLE even after using TARJAN ! any hint?


shahianshu:
20180813 10:02:54
nice question based on tarjan's algorithm , keep in mind that you can easily break away when you get 1st scc as it will give the required answer and then sort all the elements of the scc and then print them


jalaikontum:
20180723 11:20:05
AC in one go :))


s_a_k_s_h_a_m:
20180714 11:57:02
use condensation of graph


jh0n_12358:
20180627 15:33:05
After 3 hours AC in one go


aditya12legend:
20180623 17:07:47
Done with a combination of DSU and DFS 

aman_sachin200:
20180617 21:06:13
Awesome One!!!!Don't forget to print the cities in increasing order!!!!Similar problem TOUR !!:P 

ankitraj7217:
20180606 08:33:21
Weak test cases..No test cases for 0 capital city.. Last edit: 20180606 08:41:55 
Added by:  Narek Saribekyan 
Date:  20100620 
Time limit:  0.210s 
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 