#include <bits/stdc++.h>

using namespace std;

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

const int NMAX=1e5+10;
vector < int > Edge[NMAX], Components[NMAX];
int n, m, RootLevel[NMAX], NodeLevel[NMAX], niv, nrCMP;
bitset < NMAX > Seen, Belongs;
stack < int > Stack;

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

void Tarjan(int x)
{
    niv++;
    Seen[x]=1;
    Belongs[x]=1;
    Stack.push(x);
    RootLevel[x]=niv;
    NodeLevel[x]=niv;
    for(int i : Edge[x])
    {
        if(!Seen[i])
        {
            Tarjan(i);
            RootLevel[x]=min(RootLevel[x], RootLevel[i]);
        }
        else
            if(Belongs[i])
                RootLevel[x]=min(RootLevel[x], RootLevel[i]);
    }
    if(RootLevel[x]==NodeLevel[x])
    {
        nrCMP++;
        int node=0;
        do
        {
            node=Stack.top();
            Stack.pop();
            Components[nrCMP].push_back(node);
            Belongs[node]=0;
        }while(node!=x);
    }
}

int main()
{
    Read();
    for(int i=1; i<=n; i++)
        if(!Seen[i])
            niv=0, Tarjan(i);
    out<<nrCMP<<'\n';
    for(int i=1; i<=nrCMP; i++)
    {
        for(int it : Components[i])
            out<<it<<' ';
        out<<'\n';
    }
    return 0;

}