#include <iostream>

#include <cstdio>

#include <algorithm>

using namespace std;

const int N = 1e5 + ;

const int M = 5e5 + ;

#define yxy getchar()

int Tarjan_tim, now = , n, m, topp, bel;

int Stack[N], head[N], dfn[N], low[N], belong[N], Out[N];

struct Node {int u, v, nxt;} G[M];

bool vis[N];

inline int read(){

    int x = ; char c = yxy;

    while(c < '' || c > '') c = yxy;

    while(c >= '' && c <= '') x = x *  + c - '', c = yxy;

    return x;

}

inline void add(int u, int v){

    G[now].u = u; G[now].v = v; G[now].nxt = head[u]; head[u] = now ++;

}

void Tarjan(int u){

    dfn[u] = low[u] = ++ Tarjan_tim;

    vis[u] = ;

    Stack[++ topp] = u;

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

        int v = G[i].v;

        if(!dfn[v]) {

            Tarjan(v);

            low[u] = min(low[u], low[v]);

        }

        else if(vis[v]) low[u] = min(low[u], low[v]);

    }

    if(dfn[u] == low[u]){

        vis[u] = ; belong[u] = ++ bel;

        while(Stack[topp] != u){

            vis[Stack[topp]] = ;

            belong[Stack[topp]] = bel;

            topp --;

        }

        topp --;

    }

}

int main()

{

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

    for(int i = ; i <= n; i ++) head[i] = -;

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

        int u = read(); int v = read();

        add(u, v);

    }

    for(int i = ; i <= n; i ++) if(!dfn[i]) Tarjan(i);

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

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

            int v = G[i].v;

            if(belong[u] != belong[v]) Out[belong[v]] ++;

        }

    }

    int Answer();

    for(int i = ; i <= bel; i ++) if(!Out[i]) Answer ++;

    cout << Answer;

    return ;

}