#include <bits/stdc++.h>
using namespace std;
vector < int > G[100005], rev[100005], dag[100005], order;
int N, M;
int A[100005], B[100005];
bool flag[100005] = {};
int cmp[100005];
int cnt[100005] = {};

void dfs(int v)
{
    if(flag[v]) return;
    flag[v] = true;
    for(int i = 0; i < G[v].size(); i++) dfs(G[v][i]);
    order.push_back(v);
    return;
}

void rdfs(int v, int k)
{
    if(~cmp[v]) return;
    cmp[v] = k;
    for(int i = 0; i < rev[v].size(); i++) rdfs(rev[v][i], k);
    return;
}

int main()
{
    cin >> N >> M;
    for(int i = 0; i < M; i++) {
        cin >> A[i] >> B[i]; --A[i], --B[i];
        G[A[i]].push_back(B[i]);
        rev[B[i]].push_back(A[i]);
    }

    for(int i = 0; i < N; i++) dfs(i);
    int n = 0;
    fill_n(cmp, 100005, -1);
    for(int i = N - 1; i >= 0; i--) {
        if(!~cmp[order[i]]) {
            rdfs(order[i], n); n++;
        }
    }
    for(int i = 0; i < M; i++) if(cmp[A[i]] != cmp[B[i]]) cnt[cmp[B[i]]]++;
    int ans = 0;
    for(int i = 0; i < n; i++) {
        if(cnt[i] == 0) ans++;
    }
    cout << ans << endl;
    return (0);
}