#include <bits/stdc++.h>

using namespace std;

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

int n, m;

const int N = 1e5;

vector <int> a[2 * N + 1], v[2 * N + 1];
int fre1[N + 1], fre2[N + 1], ctc[N + 1];

void dfs1(int x)
{
    fre1[x] = 1;
    for(auto vecin:a[x])
    {
        if(!fre1[vecin])
        {
            fre1[vecin] = 1;
            dfs1(vecin);
        }
    }
}

void dfs2(int x)
{
    fre2[x] = 1;
    for(auto vecin:v[x])
    {
        if(!fre2[vecin])
        {
            fre2[vecin] = 1;
            dfs2(vecin);
        }
    }
}

int main()
{
    in >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        in >> x >> y;
        a[x].push_back(y);
        v[y].push_back(x);
    }
    int cnt = 0;
    for(int i = 1; i <= n; i++)
    {
        if(!ctc[i])
        {
            dfs1(i);
            dfs2(i);
            cnt++;
            for(int j = 1; j <= n; j++)
            {
                if(fre1[j] && fre2[j])
                    ctc[j] = cnt;
            }
            memset(fre1, 0, sizeof(fre1));
            memset(fre2, 0, sizeof(fre2));
        }
    }
    out << cnt << '\n';
    for(int i = 1; i <= cnt; i++)
    {
        for(int j = 1; j <= n; j++)
        {
            if(ctc[j] == i)
                out << j << ' ';
        }
        out << '\n';
    }
    return 0;
}