#include <bits/stdc++.h>

using namespace std;

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

const int NMAX=1e5+10;
int n, m, i, x, y, Niv[NMAX], niv, s[NMAX], f[NMAX], low[NMAX], nrcomp;
stack <int> ST;
vector<int> L[NMAX], C[NMAX];

void Read()
{
    in>>n>>m;
    for(i=1; i<=m; i++)
    {
        in>>x>>y;
        L[x].push_back(y);
    }
}

void dfs(int nod)
{
    niv++;
    Niv[nod]=niv;
    low[nod]=niv;
    s[nod]=1;
    f[nod]=1;
    ST.push(nod);
    for(int i : L[nod])
    {
        if(f[i]==0)
        {
            dfs(i);
            low[nod]=min(low[nod], low[i]);
        }
        else
            if(s[i])
                low[nod]=min(low[nod], low[i]);
    }
    if(Niv[nod]==low[nod])
    {
        nrcomp++;
        int x=0;
        do
        {
            x=ST.top();
            C[nrcomp].push_back(x);
            ST.pop();
            s[x]=0;
        }
        while(x!=nod);
    }
}

int main()
{
    Read();
    for(i=1; i<=n; i++)
        if(f[i]==0)
            dfs(i);
    out<<nrcomp<<'\n';
    for(int i=1; i<=nrcomp; i++)
    {
        for(int j : C[i])
            out<<j<<' ';
        out<<'\n';
    }
    return 0;
}