#include <stdio.h>
#include <vector>
using namespace std;

#define MAX 1000000

vector<int> v[MAX + 1];
bool viz[MAX + 1];

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

int main()
{
    FILE *fin, *fout;

    fin  = fopen("dfs.in", "r");
    fout = fopen("dfs.out", "w");

    int n, m, cnt = 0;

    fscanf(fin, "%d %d", &n, &m);

    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fscanf(fin, "%d %d", &x, &y);
        v[x].push_back(y);
    }


    for(int i = 1; i <= n; i++)
    {
        if(viz[i] == 0)
        {
            cnt++;
            dfs(i);
        }
    }

    fprintf(fout, "%d\n", cnt);

    //for(int i = 1; i <= cnt; i++)
        //fprintf(fout, "%d\n", sol[i]);

    return 0;
}