#include <bits/stdc++.h>
#define DIM 100005

using namespace std;

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

int n, m, k;
stack <int> s;
bitset <DIM> v;
vector <int> edges[DIM], edges1[DIM], ctc[DIM];

void dfs(int nod)
{
    v[nod] = 1;
    for(auto child : edges[nod])
        if(!v[child])
            dfs(child);
    s.push(nod);
}

void dfs1(int nod)
{
    ctc[k].push_back(nod);
    v[nod] = 1;
    for(auto child : edges1[nod])
        if(!v[child])
            dfs1(child);
}

int main()
{
    f >> n >> m;

    for(int i = 1; i <= m; i++)
    {
        int x, y;
        f >> x >> y;
        edges[x].push_back(y);
        edges1[y].push_back(x);
    }

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

    v.reset();
    while(!s.empty())
    {
        if(!v[s.top()])
        {
            k++;
            dfs1(s.top());
        }
        s.pop();
    }
    g << k << "\n";
    for(int i = 1; i <= k; i++, g << "\n")
        for(auto x : ctc[i])
            g << x << " ";

    return 0;
}