#include<fstream>
#include<vector>
#include<cstring>
using namespace std;
ifstream f ("dfs.in");
ofstream g ("dfs.out");
int n,m,nr,x,y;
vector<int>G[1000010];
bool viz[1000010];
void dfs(int x){
    viz[x]=1;
    for(int i=0;i<G[x].size();++i){
        if(!viz[G[x][i]]) dfs(G[x][i]);
    }
}
int main()
{
    f>>n>>m;
    for(int i=1;i<=m;++i){
        f>>x>>y;
        G[x].push_back(y);
    }
    for(int i=1;i<=n;++i){
        if(!viz[i]) nr++,dfs(i);
    }
    g<<nr;
}