#include <iostream>
#include <cstdio>
#include <bitset>
#include <vector>
#include <stack>

using namespace std;

const int MuchMax = 200005;
const int NodMax = 100005;
stack < int > st;
vector < int > G[MuchMax], Gt[MuchMax];
bitset < NodMax > viz;
int N, M;

void Read()
{
    scanf("%d %d", &N, &M);
    for(int i=1; i<=M; ++i)
    {
        int x, y;
        scanf("%d %d", &x, &y);
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
}

void DFS(int nod)
{
    viz[nod] = 1;
    vector < int > ::iterator it;
    for(it=G[nod].begin(); it!=G[nod].end(); ++it)
    {
        if(!viz[*it])
        {
            DFS(*it);
        }
    }

    st.push(nod);
}

void DFSt(int nod)
{
    viz[nod] = 1;
    vector < int > ::iterator it;
    for(it=Gt[nod].begin(); it!=Gt[nod].end(); ++it)
    {
        if(!viz[*it])
        {
            DFSt(*it);
        }
    }
}

int main()
{
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    Read();
    for(int i=1; i<=N; ++i)
    {
        if(!viz[i])
        {
            DFS(i);
        }
    }

    viz.reset();
    int ctc = 0;

    while(!st.empty())
    {
        int vf = st.top();
        if(!viz[vf])
        {
            DFSt(vf);
            ++ctc;
        }
        st.pop();
    }

    cout << ctc;
    return 0;
}