#include<cstdio>

#define N 100004
int sum[N];
struct node{
    int v,next;
}edge[N*2];
int rd[N],cd[N],head[N];
int n,m;
int read(){
    int x=0,f=1;char c=getchar();
    while(c>‘9‘||c<‘0‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c<=‘9‘&&c>=‘0‘){x=x*10+c-‘0‘;c=getchar();}
    return x*f;
}
int num;int ans;
void add_edge(int x,int y){
    edge[++num].v=y;edge[num].next=head[x];head[x]=num;
}
int frist[N],cnt;

int dfs(int x)
{
    if(cd[x]==0)
    {
        sum[x]++;
    }
    for(int i=head[x];i;i=edge[i].next)
    {
        if(sum[edge[i].v])sum[x]+=sum[edge[i].v];
        else sum[x]+=dfs(edge[i].v);
    }
    return sum[x];
}
int main()
{
    //freopen("chain_2016.in","r",stdin);
    //freopen("chain_2016.out","w",stdout);
    n=read();m=read();
    int a,b;
    for(int i=1;i<=m;i++)
    {
        a=read();b=read();
        add_edge(a,b);
        cd[a]++;
        rd[b]++;
    }
    for(int i=1;i<=n;i++)
    {
        if(rd[i]==0&&cd[i]!=0)
        {
            ans+=dfs(i);
        }
    }
    printf("%d",ans);
    return 0;
}