#include <cstdio>
#include <vector>

#define NMAX 100007
#define DIM 10007

using namespace std;
int n, m, a, b, t[NMAX], low[NMAX], viz[NMAX], ct = 1, nrdfs, tp[NMAX], ans, poz;
vector <int> adj[NMAX];
char buff[DIM];

void citeste(int &nr)
{
    nr = 0;
    while(buff[poz] < '0' || buff[poz] > '9')
    {
        ++poz;
        if(poz == DIM)
        {
            poz = 0;
            fread(buff, 1, DIM, stdin);
        }
    }
    while(buff[poz] >= '0' && buff[poz] <= '9')
    {
        nr = nr*10 + buff[poz]-'0';
        ++poz;
        if(poz == DIM)
        {
            poz = 0;
            fread(buff, 1, DIM, stdin);
        }
    }
}

void citire()
{
    //scanf("%d %d", &n, &m);
    citeste(n);
    citeste(m);
    for(; m; --m)
    {
        //scanf("%d %d", &a, &b);
        citeste(a);
        citeste(b);
        adj[a].push_back(b);
    }
}
void dfs(int nod)
{
    viz[nod] = nrdfs;
    t[nod] = ct;
    tp[ct] = nod;
    ++ct;
    low[nod] = t[nod];
    int sze = adj[nod].size();
    for(int i = 0; i< sze; ++i)
    {
        if(viz[adj[nod][i]] == nrdfs)
        {
            if(low[adj[nod][i]] < low[nod]) low[nod] = low[adj[nod][i]];
        }
    }
    for(int i = 0; i< sze; ++i)
    {
        if(!viz[adj[nod][i]])
        {
            dfs(adj[nod][i]);
            if(low[adj[nod][i]] < low[nod]) low[nod] = low[adj[nod][i]];
        }
    }
}
void tarjan()
{
    for(int i = 1; i<= n; ++i)
    {
        if(!viz[i])
        {
            ++nrdfs;
            dfs(i);
        }
    }
    for(int i = 1; i<= n; ++i)
    {
        int tmp = i;
        while(low[tmp] != t[tmp])
        {
            tmp = tp[low[tmp]];
        }
        low[i] = low[tmp];
    }
}
void afisare()
{
    for(int i = 1;i<= n; ++i)
    {
        if(viz[low[i]])
        {
            ans ++;
            viz[low[i]] = 0;
        }
    }
    printf("%d\n", ans);
    int it = 1;
    for(; ans; --ans)
    {
        while(viz[it]) ++it;
        for(int i = 1; i<= n; ++i)
        {
            if(low[i] == it) printf("%d ", i);
        }
        printf("\n");
        ++it;
    }
}

int main()
{
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    citire();
    tarjan();
    afisare();
    return 0;
}