#include <bits/stdc++.h>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

int n, m;
vector<int>v[100005], g[100005], answer[100005];
int viz[100005], parc[100005], top, nrc;
void DFS1(int x)
{
    viz[x] = 1;
    for(auto nod: v[x])
        if(!viz[nod])
            DFS1(nod);

    parc[++top] = x;

}
void DFS2(int x)
{
    viz[x] = 1;
    for(auto nod: g[x])
        if(!viz[nod])
            DFS2(nod);
    answer[nrc].push_back(x);
}


int main()
{
    int x, y;
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        fin >> x >> y;
        v[x].push_back(y);
        g[y].push_back(x);
    }
    for(int i = 1; i <= n; i++)
        if(!viz[i])
            DFS1(i);
    for(int i = 1; i <= n; i++)
        viz[i] = 0;
    for(int i = n; i >= 1; i--)
        if(!viz[parc[i]])
        {
            nrc++;
            DFS2(parc[i]);
        }
    fout << nrc << "\n";
    for(int i = 1; i <= nrc; i++)
    {
        for(auto nod: answer[i])
            fout << nod << " ";
        fout << "\n";

    }

    return 0;
}