#include<iostream>

#include<cstdio>

#include<cstring>

#include<cmath>

#include<bitset>

using namespace std;

const int MAXN = ;

inline int rd(){

    int x=,f=;char ch=getchar();

    while(!isdigit(ch)) {f=ch=='-'?:;ch=getchar();}

    while(isdigit(ch))  {x=(x<<)+(x<<)+ch-'';ch=getchar();}

    return f?x:-x;

}

int n,m,ans;

bitset<MAXN> a[MAXN];

int main(){

//    freopen("rank.in","r",stdin);

//    freopen("rank.out","w",stdout);

    n=rd(),m=rd();int x,y;

    while(m--){

        x=rd(),y=rd();

        a[x][y]=;

    }

    for(int k=;k<=n;k++)

        for(register int i=;i<=n;i++)

            if(a[i][k]) a[i]|=a[k];

    for(int i=;i<=n;i++){

        bool flag=;

        for(register int j=;j<=n;j++) if(i!=j)

            if(!a[i][j] && !a[j][i]) {flag=;break;}

        if(flag) ans++;

    }

    printf("%d",ans);

    return ;

}