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

const int MAXN=100001;
vector <int> a[MAXN];
int viz[MAXN], comp, n, m, x, y;

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

int main()
{
    freopen("dfs.in","r", stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d", &n, &m);
    for(int i=1; i<=m; i++)
    {
        scanf("%d %d", &x, &y);
        a[x].push_back(y);
    }
    fill(viz,viz+n,0);
    for(int i=0;i<n;i++)
        if(viz[i]==0) { comp++; dfs(i);  }
    printf("%d", comp);
    return 0;
}