#include<bits/stdc++.h>

#define N 400010

typedef long long ll;

using namespace std;

int head[*N],tot=,in[N],out[N],n,m;

struct Edge{int u,v,next;}G[N<<];

inline void addedge(int u,int v){

    G[++tot].u=u;G[tot].v=v;G[tot].next=head[u];head[u]=tot;

}

ll dp[N];

ll dfs(int u){

    if(dp[u])return dp[u];ll ans=;

    if(!out[u]&&in[u])++ans;

    for(int i=head[u];i;i=G[i].next){

        int v=G[i].v;ans+=dfs(v);

    }

    dp[u]=ans;return ans;

}

inline int read(){

    int f=,x=;char ch;

    do{ch=getchar();if(ch=='-')f=-;}while(ch<''||ch>'');

    do{x=x*+ch-'';ch=getchar();}while(ch>=''&&ch<='');

    return f*x;

}

int main(){

    n=read();m=read();

    for(int i=,u,v;i<=m;i++){

        u=read();v=read();out[u]++;in[v]++;

        addedge(u,v);

    }

    ll ans=;

    for(int i=;i<=n;i++)if(!in[i])ans+=dfs(i);

    cout<<ans<<endl;

}