#include<stdio.h>
using namespace std;
int vf[400005], urm[400005], lst [100005],viz[100001], nr = 0;
inline void adauga (int x, int y)
{

    ++nr;
    vf[nr] = y;
    urm[nr] = lst[x];
    lst[x] = nr;
}
inline void dfs (int x)
{
    int p, y;
    viz[x] = true;
    p = lst[x];
    while (p != 0)
    {
        y = vf[p];
        if (!viz[y])
            dfs(y);
        p = urm[p];
    }
}
int main ()
{
    FILE *in , *out;
    in = fopen ("dfs.in", "r");
    out = fopen ("dfs.out", "w");
    int n, m;
    fscanf (in, "%d%d", &n, &m);
    int x, y,i;
    for (i = 1; i <= m; i++)
    {
        fscanf (in, "%d%d", &x, &y);
        adauga(x, y);
    }
    int c = 0;
    for (i = 1; i <= m; i++)
    {
        if (viz[lst[i]] == 0)
        {
            c++;
            dfs(lst[i]);
        }
    }
    fprintf (out, "%d", c);
    return 0;
}