#include <bits/stdc++.h>
using namespace std;
typedef vector<int> vi;
bool v[100005];
int u,s,n,m,nr;
vector<vi> adj(100005,vi());


void dfs(int i)
{
    v[i] = true;
    for (int u = 0; u<(int)adj[i].size(); ++u)
    {
        if (!v[adj[i][u]]) dfs(adj[i][u]);
    }
}

int main()
{
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d%d",&n,&m); nr = 0;
    for (int i = 0; i<m; ++i)
    {
        scanf("%d%d",&u,&s);
        adj[u].push_back(s);
    }
    for (int i = 1; i<=n; ++i)
    {
        if (!v[i])
        {
            nr++;
            dfs(i);
        }
    }
    printf("%d",nr);
}