#include<cstdio>
#include<vector>
#include<bitset>

using namespace std;

const int NMAX = 100000+5;

void Read(),Solve(),Print();

int N,M,Nr_Comp;
vector<int> V[NMAX];
bitset<NMAX> Viz;

void DFS(int nod)
{
    vector<int>::iterator it;

    Viz[nod] = 1;

    for(it = V[nod].begin(); it != V[nod].end(); it++)
        if(!Viz[*it]) DFS(*it);
}

int main()
{
    Read();
    Solve();
    Print();

    return 0;
}

void Read()
{
    int x,y;

    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);

    scanf("%d%d",&N,&M);

    for(; M; --M)
    {
        scanf("%d%d",&x,&y);
        V[x].push_back(y);
    }
}

void Solve()
{
    int i;

    for(i = 1; i <= N; i++)
        if(!Viz[i]) DFS(i),Nr_Comp++;
}

void Print()
{
    printf("%d\n",Nr_Comp);
}