#include <iostream>
#include <fstream>
#include <vector>

using namespace std;
vector <int> g[100005];
int viz[100005];
int n,m;
void citire()
{
    scanf("%d %d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        int x,y;
        scanf("%d %d",&x,&y);
        if(x!=y)
            g[x].push_back(y);
    }
}
void dfs(int x)
{
    viz[x]=1;
    for(vector <int>::iterator it=g[x].begin();it!=g[x].end();it++)
        if(viz[*it]==0)
            dfs(*it);
}
int main()
{
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    citire();
    int k=0;
    for(int i=1;i<=n;i++)
        if(viz[i]==0)
            {k++;
            dfs(i);}
    printf("%d",k);
    return 0;
}