#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

#define ALB 1
#define GRI 2
#define NEGRU 3

vector< vector<int> > graph;
vector<int> c, d, f, pi;
int timp;


void explorare(int node)
{
    d[node] = timp++;
    c[node] = GRI;
    for(int i = 0; i < graph[node].size(); i++)
    {
        if(c[graph[node][i]] == ALB)
        {
            pi[graph[node][i]] = node;
            explorare(graph[node][i]);
        }
    }
    c[node] = NEGRU;
    f[node] = timp++;
}

int dfs()
{
    c.resize(graph.size());
    d.resize(graph.size());
    f.resize(graph.size());
    pi.resize(graph.size());

    for(int i = 1; i < graph.size(); i++)
    {

        c[i] = ALB;
        pi[i] = 0;
    }

    timp = 0;
    for(int i = 1; i < graph.size(); i++)
    {
        if(c[i] == ALB)
        {
            explorare(i);
        }
    }

    return (int)count(pi.begin(), pi.end(), 0) - 1;
}


int main()
{
    ifstream in ("dfs.in");
    ofstream out ("dfs.out");
    int n, m, x, y;
    in >> n >> m;
    graph.resize(n + 1);
    for(int i = 0; i < m; i++)
    {
        in >> x >> y;
        graph[x].push_back(y);
    }
    out << dfs();
    out.close();
    in.close();
    return 0;
}