#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");

main()
{
    long n, m, x, y, cm, nr;
    long *t;
    fin>>n>>m;
    t = new long[n+1];
    cm = m;
    for(long i=1; i<=n; i++) t[i] = 0;
    while(cm--)
    {
        fin>>x>>y;
        t[y]=x;
    }
    fin.close();
    nr = 0;
    for(long i=1; i<=n; i++)
        if(t[i]==0) nr++;
    fout<<nr;
    delete t; fout.close();
}