#include <iostream>

#include <vector>

#include <stack>

#include <cstring>

#define maxn 100005

using namespace std;

int n, m;

vector<int> g[maxn], g2[maxn];

int indegree[maxn];

int timer = , cnter = ;

int dfn[maxn], low[maxn], scc[maxn];

stack<int> sta;

bool insta[maxn];

void dfs(int v)

{

    /*

    low[v]=min{

        dfn[v],

        low[w], 存在有向边(v,w)且搜索到v时w尚未被搜索到

        dfn[w]  存在有向边(v,w)且搜索到v时w在栈内

    }

    */

    low[v] = dfn[v] = ++timer;

    sta.push(v);

    insta[v] = true;

    for (int i = ; i < g[v].size(); i++)

    {

        int w = g[v][i];

        if (!dfn[w])

        {

            dfs(w);

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

        }

        else if (insta[w])

        {

            low[v] = min(low[v], dfn[w]);

        }

    }

    if (dfn[v] == low[v])

    {

        ++cnter;

        int t;

        do

        {

            t = sta.top();

            sta.pop();

            insta[t] = false;

            scc[t] = cnter;

        } while (t != v);

    }

}

void tarjan_scc()

{

    for (int i = ; i <= n; i++)

    {

        if (!dfn[i])

            dfs(i);

    }

}

void contract()

{

    for (int v = ; v <= n; v++)

    {

        for (int i = ; i < g[v].size(); i++)

        {

            // 对于边(v,w)，若v与w不在同一SCC，则该边在缩点后的新图为(scc[v],scc[w])

            int w = g[v][i];

            if (scc[v] != scc[w])

            {

                g2[scc[v]].push_back(scc[w]);

                indegree[scc[w]]++;

            }

        }

    }

}

int main()

{

    ios::sync_with_stdio(false);

    cin >> n >> m;

    int u, v;

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

    {

        cin >> u >> v;

        g[u].push_back(v);

    }

    tarjan_scc();

    contract();

    // 统计得到的DAG中入度为0的点

    int ans = ;

    for (int i = ; i <= cnter; i++)

    {

        if (!indegree[i])

            ans++;

    }

    cout << ans << endl;

    return ;

}