#include <bits/stdc++.h>
using namespace std;
int n, m;
bool g[105][105];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int u, v;
        cin >> u >> v;
        g[u][v] = true;
    }
    for (int k = 1; k <= n; k++)
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++)
                g[i][j] = g[i][j] || g[i][k] && g[k][j];
    int ans = 0;
    for (int i = 1; i <= n; i++)
    {
        bool flag = true;
        for (int j = 1; j <= n; j++)
            if (i != j && !g[i][j] && !g[j][i])
            {
                flag = false;
                break;
            }
        ans += flag;
    }
    cout << ans << endl;
    return 0;
}