#include<fstream>
#include<vector>
using namespace std;
#define NMAX 100010
ifstream f ("dfs.in");
ofstream g ("dfs.out");
vector <int> A[NMAX];
int viz[NMAX], V[NMAX], N, M, x, y, i, nr=0;

void dfs(int x)
{
     viz[x]=1;
     for(i=0;i<A[x].size();i++)
       if(!viz[A[x][i]]) dfs(A[x][i]);
}

int main()
{
    f>>N>>M;
    for(i=1;i<=M;i++) f>>x>>y, A[x].push_back(y);
    for(i=1;i<=N;i++) if(!viz[i]) dfs(i), nr++;
    g<<nr;
    g.close();
    return 0;
}