#include <fstream>
#include <algorithm>
#include <vector>
#include <list>
#include <stack>
using namespace std;

int nodes,edges,counter,stronglyConnectedComponents;
vector< list<int> > graph;
stack<int> nodeStack;
vector<bool> inStack;
vector<int> index,lowlink;
vector< vector<int> > solution;

void read();
void tarjan(int toVisit);
void write();

int main() {
	read();
	
	for(int i=1;i<=nodes;i++)
		if(!index.at(i))
			tarjan(i);
	
	write();	
	
	return (0);
}

void read() {
	ifstream in("ctc.in");
	int from,to;
	
	in >> nodes >> edges;
	graph.resize(nodes+1);
	inStack.resize(nodes+1);
	index.resize(nodes+1);
	lowlink.resize(nodes+1);
	
	for(int i=1;i<=edges;i++) {
		in >> from >> to;
		
		graph.at(from).push_back(to);
	}
	
	in.close();
}

void tarjan(int toVisit) {
	index.at(toVisit) = ++counter;
	lowlink.at(toVisit) = counter;
	
	nodeStack.push(toVisit);
	//out << "Am introdus in coada " << toVisit << endl;
	inStack.at(toVisit) = true;
	
	for(list<int>::iterator it=graph.at(toVisit).begin();it!=graph.at(toVisit).end();it++)
		if(!index.at(*it)) {	// daca nu a fost vizitat
			tarjan(*it);
			lowlink.at(toVisit) = min(lowlink.at(toVisit),lowlink.at(*it));
		}
		else
			if(inStack.at(*it))
				lowlink.at(toVisit) = min(lowlink.at(toVisit),lowlink.at(*it));
	
	if(lowlink.at(toVisit) == index.at(toVisit)) {
		//out << "Componenta tare conexa:" << endl;
		int toPrint;
		vector<int> oneSolution;
		
		while(toPrint != toVisit) {
			toPrint = nodeStack.top();
			nodeStack.pop();
			inStack.at(toPrint) = false;
			
			//out << toPrint << " ";
			oneSolution.push_back(toPrint);
		}
		
		solution.push_back(oneSolution);
		stronglyConnectedComponents++;
		
		//out << endl;
	}
	
}

void write() {
	ofstream out("ctc.out");
	
	out << stronglyConnectedComponents << endl;
	
	out.close();
}