/*
* Strongly Connected Component
* Algorithm : Tarjan's Algorithm
* Order : O( V+E )
*/
#include<stdio.h>
#include<string.h>
#include<vector>
#include<stack>
#include<algorithm>
using namespace std;
#define MAX 4007
#define pb push_back
long N,M;
vector<long> Edge[MAX+7];
bool Visit[MAX+7];
bool InStk[MAX+7];
long Low[MAX+7],I;
long Ind[MAX+7];
stack<long> Stk;
void SCC( long u )
{
Visit[u] = true;
InStk[u] = true;
Ind[u] = ++I;
Low[u] = I;
Stk.push( u );
long i;
for( i=0;i<Edge[u].size();i++){
long v = Edge[u][i];
if( !Visit[v] ){
SCC( v );
Low[u] = min( Low[u],Low[v] );
}
else if( InStk[v] ){
Low[u] = min( Low[u],Ind[v] );
}
}
if( Low[u]!=Ind[u] ) return;
// found new component
while( Stk.top()!=u ){
long v = Stk.top();
Stk.pop();
InStk[v] = false;
}
Stk.pop();
InStk[u] = false;
}
int main( void )
{
long i,j,u,v,Icase,k = 0;
//freopen("text1.txt","r",stdin );
scanf("%ld%ld",&N,&M );
for( i=1;i<=M;i++){
scanf("%ld%ld",&u,&v );
Edge[u].pb( v );
}
for( i=1;i<=N;i++){
if( Visit[i] ) continue;
SCC( i );
}
return 0;
}
