#include <stdio.h>
#include <stdlib.h>
#include <vector>

using namespace std;

#define MAX_V    2001
#define FOR(t,i,n) for(t i=0;i<n;i++)
#define FIT(t,i,c) for(t::iterator i=c.begin();i!=c.end();i++)

typedef vector<long> _vector_long;

_vector_long adj[MAX_V];            //Adjacency vector representation of graph
_vector_long adj_t[MAX_V];            //Adjacency vector representation of transpose of graph
long order[MAX_V], finish[MAX_V], scc_number[MAX_V];
long t_time, scc_num;
char color[MAX_V];
char scc_in[MAX_V];            //1 if there are outgoing vertices from this SCC
long V, E;

int compare(const void *a, const void *b)
{
    long aa = *(long *)a;
    long bb = *(long *)b;
    return finish[bb]-finish[aa];
}

void DFS_visit(_vector_long adj[], long u)
{
    scc_number[u]=scc_num;
    color[u]=0;

    t_time++;
    FIT(_vector_long,i,adj[u]) {
        if(color[*i]==1) {
            DFS_visit(adj, *i);
        }
    }
    finish[u]=t_time=t_time+1;
}

long DFS(_vector_long adj[])
{
    long count=0;            //Keeps a count of the number of DFS forests
    scc_num=0;
    t_time=0;
    FOR(long,i,V) 
        color[i]=1;        //1 --> NOT VISITED, 0 --> VISITED
    FOR(long,i,V) {
        if(color[order[i]]==1) {
            count++; 
            DFS_visit(adj, order[i]);
            scc_num++;
        }
    }
    return count;
}

int main()
{
    scanf("%ld %ld", &V, &E);
    FOR(long,i,E) {
        long f, t;
        scanf("%ld %ld", &f, &t);
        adj[f-1].push_back(t-1);
        adj_t[t-1].push_back(f-1);
    }

    //Compute the number of strongly connected components
    FOR(long, i, V) order[i]=i;    //Initial order for DFS, numerical
    //Compute the finish times
    DFS(adj);
    //Reorder order according to finish
    qsort(order, V, sizeof(long), compare);

    long count=DFS(adj_t);
    //memset(scc_in, 0, sizeof(scc_in));    --- scc_in made global

    FOR(long,i,V) 
        FIT(_vector_long,j,adj[i]) {
            if(scc_number[i]!=scc_number[*j]) {
                scc_in[scc_number[*j]]=1;
            }
        }

    long ans=0;
    FOR(long,i,count) ans+=scc_in[i];
    count-=ans;
    printf("%ld\n", count);
    return 0;
}