#pragma GCC optimize(3)

#include<bits/stdc++.h>

using namespace std;

const int N=;

vector<int> G[N];

stack<int> S;

int pre[N],lowlink[N],sccno[N],dfs_clock,scc_cnt,ind[N];

const int bsz=<<;

char bf[bsz],*head,*tail;

inline char gc(){

    if(head==tail){

        int l=fread(bf,,bsz,stdin);

        tail=(head=bf)+l;

    }

    return *head++;

}

inline int read(){

    int x=;char c=gc();

    while(!isdigit(c))c=gc();

    for(;isdigit(c);c=gc())x=x*+c-'';

    return x;

}

inline void write(int x){

    if(x>=)write(x/);

    putchar(x%+'');

}

void dfs(int in){

    pre[in]=lowlink[in]=++dfs_clock;

    S.push(in);

    int num=G[in].size();

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

        int v=G[in][i];

        if(!pre[v]){

            dfs(v);

            lowlink[in]=min(lowlink[in],lowlink[v]);

        }

        else if(!sccno[v])

            lowlink[in]=min(lowlink[in],pre[v]);

    }

    if(lowlink[in]==pre[in]){

        scc_cnt++;

        while(){

            int x=S.top();

            S.pop();

            sccno[x]=scc_cnt;

            if(x==in)

                break;

        }

    }

}

int main(){

    int N=read(),M=read(),i,j,a,b;

    for(i=;i<M;i++){

        a=read();

        b=read();

        G[a].push_back(b);

    }

    dfs_clock=scc_cnt=;

    memset(sccno,,sizeof sccno);

    memset(pre,,sizeof pre);

    for(i=;i<=N;i++)

        if(!pre[i])

            dfs(i);

    memset(ind,,sizeof ind);

    for(i=;i<=N;i++){

        a=G[i].size();

        for(j=;j<a;j++)

            if(sccno[i]!=sccno[G[i][j]])

                ind[sccno[G[i][j]]]++;

    }

    for(a=,i=;i<=scc_cnt;i++)

        if(!ind[i])

            a++;

    write(a);

    return ;

}