#include <bits/stdc++.h>

using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

int n,m,s,x,k,y,viz[100200];
vector <int> edges[100200];

void dfs(int x)
{
    viz[x]=k;
    for(auto y:edges[x])
        if(viz[y]==0)
            dfs(y);
}

int32_t main()
{
    f>>n>>m;
    for(int i=1; i<=m; i++)
        f>>x>>y, edges[x].push_back(y);
    for(int i=1; i<=n; i++)
        if(viz[i]==0)
            k++, dfs(i);
    g<<k;
    return 0;
}