#include <cstdio>
#include <vector>
#include <cstring>
#include <algorithm>

using namespace std;

const int Nmax = 100010;

int n , m , x , y  , nr;
int v[Nmax];

bool marked[Nmax];

vector < int > g[2][Nmax] , aux;
vector < pair < int , int > > ctc;

void dfs(int node , int ind)
{
    marked[node] = true;

    for (int i = 0; i < g[ind][node].size(); ++i)
        if (!marked[g[ind][node][i]])
            dfs(g[ind][node][i] , ind);

    (ind) ? ctc.push_back({nr , node}) : aux.push_back(node);
}

void sorteaza(int ind)
{
    memset(marked , false , sizeof(marked));

    for (int i = 1; i <= n; ++i)
        if (!marked[v[i]])
        {
            if (ind) nr++;
            dfs(v[i] , ind);
        }
}

int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);

    for (scanf("%d %d", &n, &m); m; --m)
    {
        scanf("%d %d", &x, &y);
        g[0][x].push_back(y);
        g[1][y].push_back(x);
    }

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

    reverse(aux.begin() , aux.end());
    for (int i = 1; i <= n; ++i)
        v[i] = aux[i-1];
    sorteaza(1);

    printf("%d\n%d ", nr , ctc[0].second);
    for (int i = 1; i < ctc.size(); ++i)
    {
        if (ctc[i].first != ctc[i-1].first) printf("\n");
        printf("%d ", ctc[i].second);
    }

    return 0;
}