#include <stdio.h>
#include <bitset>
#include <vector>
#include <cstring>
#include <algorithm>
#define NMAX 100005

using namespace std;

vector <int> G[NMAX], Gt[NMAX];
bitset <NMAX> viz, viz2;
int sol[NMAX], k;

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);
    sol[++k] = nod;
}

void dfs2(int nod){
    viz2[nod] = 1;
    //printf("%d ", nod);
    vector <int> :: iterator it;
    for(it = Gt[nod].begin(); it != Gt[nod].end(); ++it)
        if(!viz2[*it])
            dfs2(*it);
}

int main(){
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    int N, M, x, y, nr = 0;
    scanf("%d %d", &N, &M);
    for(int i = 1; i <= M; ++i){
        scanf("%d %d", &x, &y);
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
    for(int i = 1; i <= N; ++i)
        if(!viz[i])
            dfs(i);
    for(int i = N; i >= 1; --i)
        if(!viz2[sol[i]]){
            dfs2(sol[i]);
            ++nr;
            //printf("\n");
        }
    printf("%d\n", nr);
    return 0;
}