#include <algorithm>
#include <fstream>
#include <vector>

using namespace std;

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

const int nmax = 100005;
int n, m, fr[nmax], ind;
vector<int> s, v[nmax], v2[nmax];
vector< vector<int> > ctc(nmax);

void dfs(int nod, vector<int> a[], vector<int> &add)
{
    fr[nod] = 1;
    for(auto x : a[nod])
        if(!fr[x])
            dfs(x, a, add);

    add.push_back(nod);
}

int main()
{
    f >> n >> m;
    for(int i = 1; i <= m; i ++)
    {
        int x, y; f >> x >> y;
        v[x].push_back(y);
        v2[y].push_back(x);
    }

    for(int i = 1; i <= n; i ++)
        if(!fr[i])
            dfs(i, v, s);

    reverse(s.begin(), s.end());

    for(int i = 1; i <= n; i ++)
        fr[i] = 0;

    for(int i = 0; i < s.size(); i ++)
        if(!fr[s[i]])
            ind ++, dfs(s[i], v2, ctc[ind]);

    g << ind << '\n';
    for(int i = 1; i <= ind; i ++, g << '\n')
        for(auto x : ctc[i])
            g << x << " ";
    return 0;
}