#include<fstream>
#include<vector>
#include<stack>
using namespace std;
vector<int> L[100005], ct[100005];
stack<int> s;
bool is[100005];
int n, m, i, x, y, niv[100005], low[100005], lvl, nct, j;
void dfsc(int nod)
{
    s.push(nod);
    is[nod]=1;
    lvl++;
    low[nod]=lvl;
    niv[nod]=lvl;
    for(int i=0; i<L[nod].size(); i++)
    {
        int fiu=L[nod][i];
        if(niv[fiu]==0)
        {
            dfsc(fiu);
            low[nod]=min(low[nod], low[fiu]);
        }else
        {
            if(is[fiu]==1)
                low[nod]=min(low[nod], low[fiu]);
        }
    }
    if(niv[nod]==low[nod])
    {
        nct++;
        do
        {
            x=s.top();
            ct[nct].push_back(x);
            s.pop();
            is[x]=0;
        }
        while(x!=nod);
    }
}
ifstream in("ctc.in");
ofstream out("ctc.out");
int main()
{
    in>>n>>m;
    for(i=1; i<=m; i++)
    {
        in>>x>>y;
        L[x].push_back(y);
    }
    for(i=1; i<=n; i++)
    {
        if(niv[i]==0)
            dfsc(i);
    }
    out<<nct<<"\n";
    for(i=1; i<=nct; i++)
    {
        for(j=0; j<ct[i].size(); j++)
            out<<ct[i][j]<<" ";
        out<<"\n";
    }
    return 0;
}