#include <bits/stdc++.h>
#define FOR(n) for(int i=1;i<=n;++i)
using namespace std;

ifstream fin("dfs.in");
ofstream fout("dfs.out");

const int NMAX = 1e5+5;
vector<int>adj[NMAX];
bool viz[NMAX];
int n, m, ans;

inline void dfs(const int &x)
{
    stack<int>s;
    s.push(x);
    while(!s.empty())
    {
        int i = s.top();
        for(auto itr : adj[i])
        {
            if(!viz[itr])
            {
                s.push(itr);
                viz[itr] = 1;
            }
        }
        s.pop();
    }
}

inline void solve()
{
    for(int i=1;i<=n;++i)
    {
        if(viz[i] == 0)
        {
            dfs(i);
            ans++;
        }
    }
    fout << ans;
}

int main()
{
    fin >> n >> m;
    FOR(m)
    {
        int x, y;
        fin >> x >> y;
        adj[x].push_back(y);
    }
    solve();
}