#include <fstream>
#include <vector>
#include <stack>

#define NMax 100010

using namespace std;

int nodes, edges, inc, nrctc;
bool mark[NMax];
stack<int> pre;
vector<int> G[NMax], Gr[NMax], sol[NMax];

void DFS(int node)
{
    mark[node] = true;
    pre.push(++inc);

    for (vector<int>::it = G[node].begin(); it != G[node].end(); it++)
        if (!mark[*it])
            DFS[*it];
}

void DFSk(int node)
{
    mark[node] = true;
    sol[nrctc].push_back(node);

    for (vector<int>::it = Gr[node].begin(); it != Gr[node].end(); it++)
        if (!mark[*it])
            DFSk[*it];
}

int main()
{
    f>>nodes>>edges;

    int n1, n2;
    for (int i=1; i<=edges; i++) {
        f>>n1>>n2;

        G[n1].push_back(n2);
        Gr[n2].push_back(n1);
    }

    for (int i=1; i<=nodes; i++)
        if (!mark[i])
            DFS(i);

    memset(mark, false, sizeof(mark));

    while (!pre.empty()) {
        if (!mark[i]) {
            nrctc++;

            DFSk(pre.top());

            pre.pop();
        }
    }

    g<<nrctc<<"\n";

    int j=1;

    for (int i=1; i<=nrctc; i++) {

    }

    return 0;
}