#include <fstream>
#include <limits.h>
#include <vector>
#include <queue>

#define nMax 100001
#define pb push_back
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int n, m, Sol;
int viz[nMax];
vector<int> G[nMax];
void read()
{
    int a, b;
    fin>>n>>m;

    for(int i=1;i<=m;i++)
    {
        fin>>a>>b;
        G[a].pb(b);
    }
}
void dfs(int node)
{
    viz[node]=1;

    for(vector<int>::iterator it=G[node].begin();it!=G[node].end();it++)
    {
        int fiu=*it;
        if(viz[fiu]==0)
            dfs(fiu);
    }
}
void solve()
{
    for(int i=1;i<=n;i++)
    {
        if(viz[i]==0)
        {
            Sol++;
            dfs(i);
        }
    }
}
void write()
{
    fout<<Sol;
}
int main()
{
    read();
    solve();
    write();
    return 0;
}