#include<stdio.h>
#include<string.h>
#define nmax 100001

int n,m,st[nmax],ns,viz[nmax],cont;

struct nod
{
    int drum;
    nod *urm;
} *l[nmax] , *lt[nmax];

void DF1(int);
void DF2(int);
void add(nod *&inc,int info)
{
    nod *p=new nod;
    p->drum=info;
    p->urm=inc;
    inc=p;
}

int main()
{
    int a,b;
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;++i)
        {
            scanf("%d%d",&a,&b);
            add(l[a],b);
            add(lt[b],a);
        }
    
    for(int i=1;i<=n;++i)
        if (!viz[i])
            DF1(i);
            
    memset(viz,0,sizeof(viz));
    
    for(int i=n;i;--i)
        if (!viz[st[i]])
            {
                DF2(st[i]);
                ++cont;
                //printf("\n");
            }
    printf("%d\n",cont);
    return 0;
}

void DF1 (int x)
{
    nod *p=l[x];
    viz[x]=1;
    
    for(;p;p=p->urm)
        if (!viz[p->drum])
            DF1(p->drum);
    
    st[++ns]=x;
    
}

void DF2(int x)
{
    nod *p=lt[x];
    viz[x]=1;
    //printf("%d ",x);
    for(;p;p=p->urm)
        if (!viz[p->drum])
            DF2(p->drum);
}