#include<bits/stdc++.h>

using namespace std;
int n,m,i,v[100005],nr,x,y;
vector <int> mu[100005];
ifstream in("dfs.in");
ofstream out("dfs.out");
void dfs(int x)
{
    int vec;
    v[x]=1;
    for (int i=0; i<mu[x].size(); i++)
    {
        vec=mu[x][i];
        if (v[vec]==0)
            dfs(vec);
    }
}
int main()
{
    in>>n>>m;
    for (i=1; i<=m; i++)
    {
        in>>x>>y;
        mu[x].push_back(y);
    }
    for (i=1; i<=n; i++)
        if (v[i]==0)
        {
            nr++;//cout<<i<<" ";
            dfs(i);
        }
    out<<nr;
}