#include <iostream>
#include <stack>
#include <stdio.h>
#include <vector>
using namespace std;
#define NMAX 100005

vector <int> g1[NMAX], g2[NMAX], ctc[NMAX];
bool v1[NMAX], v2[NMAX];
stack <int> a1, a2;

///sortare topologica
///cand citesc construiesc inca un graf opus care o sa contina drumurile inverse.

void s_topologica1(int nod)
{
    v1[nod]=1;
    for(int i=0; i<g1[nod].size(); i++)
        if(v1[g1[nod][i]]==0)
            s_topologica1(g1[nod][i]);

    a1.push(nod);
}

void s_topologica2(int nod)
{
    v2[nod]=1;
    for(int i=0; i<g2[nod].size(); i++)
        if(v2[g2[nod][i]]==0)
            s_topologica2(g2[nod][i]);

    a2.push(nod);
}

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

    int n, m, x, y, nr=0;
    scanf("%d %d \n", &n, &m);

    for(int i=1; i<=m; i++)
    {
        scanf("%d %d \n", &x, &y);
        g1[x].push_back(y);
        g2[y].push_back(x);
    }

    for(int i=1; i<=n; i++)
        if(v1[i]==0)
            s_topologica1(i);

    while(!(a1.empty()))
    {
        if(v2[a1.top()]==0)
        {
            s_topologica2(a1.top());
            nr++;
        }
        while(!(a2.empty()))
        {
            ctc[nr].push_back(a2.top());
            a2.pop();
        }
        a1.pop();
    }

    cout<<nr<<endl;
    for(int i=1; i<=nr; i++)
    {
        for(int j=0; j<ctc[i].size(); j++)
            printf("%d ", ctc[i][j]);
        printf("\n");
    }

    return 0;
}