#include <bits/stdc++.h>
using namespace std;

typedef pair<int, int> pii;
#define fi first 
#define se second
#define pb push_back

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

const int N = 1e5+5;

int n, k;
vector<int> e[N];
bool b[N];

void read();
void dfs(int);

int main()
{
    read();
    for (int i = 1; i <= n; i++)
        if (!b[i]) k++, dfs(i);
    
    g << k;

    return 0;
}

void read()
{
    int m;
    f >> n >> m;
    while (m--){
        int a, b; f >> a >> b;
        e[a].pb(b); 
    }
}
void dfs(int nod){
    b[nod] = 1;
    for (auto it: e[nod])
        if (!b[it]) dfs(it);
}