#include<iostream>
#include<cstdio> 
#include<cstring>
#include<algorithm>
#define MAXN 100000+15
using namespace std;
int n,m,tot,tim,top,sumcol,ans,bns;
int to[MAXN],from[MAXN],net[MAXN],x[MAXN],col[MAXN],into[MAXN],out[MAXN];
int dfn[MAXN],low[MAXN],vis[MAXN],stack[MAXN],visstack[MAXN];
void add(int u,int v){
    to[++tot]=v;x[tot]=u;net[tot]=from[u];from[u]=tot;
}
void tarjin(int now){
    low[now]=dfn[now]=++tim;
    stack[++top]=now;
    visstack[now]=1;
    vis[now]=1;
    for(int i=from[now];i;i=net[i])
        if(visstack[to[i]])
            low[now]=min(low[now],dfn[to[i]]);
        else if(!vis[to[i]]){
            tarjin(to[i]);
            low[now]=min(low[now],low[to[i]]);
        }
    if(dfn[now]==low[now]){
        sumcol++;
        col[now]=sumcol;
        while(stack[top]!=now){
            col[stack[top]]=sumcol;
            visstack[stack[top]]=0;
            top--;
        }
        visstack[now]=0;
        top--;
    } 
}
int T;
int main(){
    while(scanf("%d%d",&n,&m)!=EOF){
        top=0;tot=0;sumcol=0;tim=0;
        ans=0;bns=0;
        memset(to,0,sizeof(to));
        memset(low,0,sizeof(low));
        memset(dfn,0,sizeof(dfn));
        memset(vis,0,sizeof(vis));
        memset(col,0,sizeof(col));
        memset(net,0,sizeof(net));
        memset(out,0,sizeof(out));
        memset(into,0,sizeof(into));
        memset(from,0,sizeof(from));
        memset(stack,0,sizeof(stack));
        memset(visstack,0,sizeof(visstack));
        for(int i=1;i<=m;i++){
            int a,b;
            cin>>a>>b;
            add(a,b);
        }
        for(int i=1;i<=n;i++)
            if(!vis[i])    tarjin(i);
        if(sumcol==1){
            cout<<"0"<<endl;
            continue;
        }
        for(int i=1;i<=tot;i++)
            if(col[to[i]]!=col[x[i]]){
                into[col[to[i]]]++;
                out[col[x[i]]]++;
            }
        for(int i=1;i<=sumcol;i++){
            if(into[i]==0)    ans++;
            if(out[i]==0)    bns++;
        }
        cout<<max(ans,bns)<<endl;
    }
}