#include <bits/stdc++.h>
#define NMAX 100009

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int>g[NMAX];
vector <int>gt[NMAX];
int  uz[NMAX], lowlink[NMAX], cnt, cnt1;
vector <int>sol[NMAX];

int i,lg,nr,n,j,m;
int s[NMAX];
void citire();
void dfs(int k);
void dfs1(int k);
void reset();
int main()
{
    citire();
    for(i=1; i<=n; i++)
        if(!uz[i])
            dfs(i);



    fout<<nr<<'\n';
    for(i=1; i<=nr; i++)
    {
        for(j=0; j<sol[i].size(); j++)
            fout<<sol[i][j]<<" ";

        fout<<'\n';
    }
    return 0;
}
void citire()
{
    int i,j,x,y;
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        g[x].push_back(y);
        gt[y].push_back(x);

    }

}
void dfs(int k)
{
    int i;
    uz[k]= ++cnt;
    lowlink[k] = cnt;
    s[++lg]=k;
    for(i=0; i<g[k].size(); i++)
    {
        if(!uz[g[k][i]])

            dfs(g[k][i]);

        if(uz[g[k][i]] > 0)
            lowlink[k] = min(lowlink[k],lowlink[g[k][i]]);

    }
    if(uz[k] == lowlink[k])
    {
        nr++;
        do
        {
            sol[nr].push_back(s[lg]);
            uz[s[lg]] = -1;
        }
        while(s[lg--] != k);
    }

}

void reset()
{
    int i;
    for(i=0; i<NMAX; i++)
        uz[i]=0;
}