#include <iostream>
#include <queue>
#include <vector>
using namespace std;

int N, M;
vector<vector<int>> adj(100001);
vector<bool> marked(100001, false);

void dfs(int source){
	for(int i = 0; i < adj[source].size(); i++){
		if(!marked[adj[source][i]]){
			marked[adj[source][i]] = true;
			dfs(adj[source][i]);
		}
	}
}

int main(){
	int from, to, cnt = 0;
	freopen("dfs.in", "r", stdin);
	freopen("dfs.out", "w", stdout);
	scanf("%d%d", &N, &M);
	for(int i = 0; i < M; i++){
		scanf("%d%d", &from, &to);
		adj[--from].push_back(--to);
	}
	for(int i = 0; i < N; i++){
		if(!marked[i]){
			dfs(i);
			cnt ++ ;
		}
	}
	printf("%d\n", cnt);
	return 0;
}