// http://infoarena.ro/problema/ctc
#include <fstream>
#include <iostream>
#include <vector>
#include <list>
using namespace std;

int nodes,edges;
vector< list<int> > graph;
vector< list<int> > TGraph;
vector<bool> visit;
list<int> order;

void read();
void topologicalSort();
	void depthFirst(int toVisit);
void createSecondGraph();
void depthFirstT(int toVisit);
void write();

ofstream out("ctc.out");

int main() {
	read();
	topologicalSort();
	createSecondGraph();
	write();

	return (0);
}

void read() {
	ifstream in("ctc.in");
	int from,to;

	in >> nodes >> edges;
	graph.resize(nodes+1);
	TGraph.resize(nodes+1);
	visit.resize(nodes+1);

	for(int i=1;i<=edges;i++) {
		in >> from >> to;

		graph.at(from).push_back(to);
	}

	in.close();
}

void topologicalSort() {
	for(int i=1;i<=nodes;i++)
		if(!visit.at(i))
			depthFirst(i);
}

void depthFirst(int toVisit) {
	visit.at(toVisit) = true;

	for(list<int>::iterator it=graph.at(toVisit).begin();it!=graph.at(toVisit).end();it++)
		if(!visit.at(*it))
			depthFirst(*it);

	order.push_front(toVisit);
}

void createSecondGraph() {
	for(int i=1;i<=nodes;i++)
		for(list<int>::iterator it=graph.at(i).begin();it!=graph.at(i).end();it++)
			TGraph.at(*it).push_back(i);
}

void depthFirstT(int toVisit) {
	visit.at(toVisit) = true;
	//out << toVisit << " ";

	for(list<int>::iterator it=TGraph.at(toVisit).begin();it!=TGraph.at(toVisit).end();it++)
		if(!visit.at(*it))
			depthFirstT(*it);
}

void write() {
	int stronglyConnectedComponents = 0;
	visit.assign(nodes+1,false);
	
	//out << endl;
	
	for(list<int>::iterator it=order.begin();it!=order.end();it++) {
		if(!visit.at(*it)) {
			depthFirstT(*it);
			stronglyConnectedComponents++;
			//out << endl;
		}
	}
	
	//out.seekp(0);

	out << stronglyConnectedComponents;
	out.close();
}