#include <fstream>
#include <vector>
using namespace std;

ifstream cin("dfs.in");
ofstream cout("dfs.out");
#define MAXN 100005
#define INF 0x3f3f3f3f

vector<int> graf[MAXN];
bool fol[MAXN];
int n,m,i,j,x,y,nr;

void dfs(int nod)
{
    for(int i=0; i<graf[nod].size(); i++)
        if( !fol[ graf[nod][i] ] )
        {
            fol[ graf[nod][i] ] = true;
            dfs( graf[nod][i] );
        }
}

int main()
{
    cin>>n>>m;
    for(i=1; i<=m; i++)
    {
        cin>>x>>y;
        graf[x].push_back(y);
    }
    for(i=1; i<=n; i++)
        if(!fol[i])
            dfs(i), nr++;

    cout<<nr;
    return 0;
}