#include <cstdio>
#include <vector>
#define NMAX 100005
using namespace std;

vector<int> G[NMAX];
int N, M, cnt;
bool viz[NMAX];

void read(void)
{
	int x, y;
	FILE *f = fopen("dfs.in", "r");
	
	fscanf(f, "%d%d", &N, &M);
	while(M--)
		fscanf(f, "%d%d", &x, &y),
		G[x].push_back(y);
		
	fclose(f);
}

void DFS(int nod)
{
	viz[nod] = 1;
	for(int i = 0; i < G[nod].size(); ++i)
		if(!viz[G[nod][i]])
			DFS(G[nod][i]);
}
void solve(void)
{
	for(int i = 1; i <= N; ++i)
		if(!viz[i])
			++cnt, DFS(i);
}

void print(void)
{
	FILE *g = fopen("dfs.out", "w");
	fprintf(g, "%d\n", cnt);
	
	fclose(g);
}

int main(void)
{
	read();
	solve();
	print();
	
	return 0;
}