#include <bits/stdc++.h>

using namespace std;

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

const int N=100010;

int n, m, disc[N], low[N], t;
bitset<N> b, vis;
vector<int> v[N];
stack<int> s;
vector<vector<int>> sol;

void ctc(int );

int main()
{
    inf>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x, y;
        inf>>x>>y;
        v[x].push_back(y);
    }
    for(int i=1; i<=n; i++)
        disc[i]=low[i]=-1;
    for(int i=1; i<=n; i++)
        if(!vis[i])
            ctc(i);
    outf<<sol.size()<<'\n';
    for(auto c:sol)
    {
        for(auto it:c)
            outf<<it<<' ';
        outf<<'\n';
    }
    return 0;
}

void ctc(int nod)
{
    vis[nod]=true;
    disc[nod]=low[nod]=++t;
    s.push(nod);
    b[nod]=1;
    for(auto it:v[nod])
    {
        if(disc[it]==-1)
        {
            ctc(it);
            low[nod]=min(low[nod], low[it]);
        }
        else
        {
            low[nod]=min(low[nod], disc[it]);
        }
    }

    if(low[nod]==disc[nod])
    {
        int tp=-1;
        vector<int> cctc;
        do
        {
            tp=s.top();
            s.pop();
            b[tp]=0;
            cctc.push_back(tp);
        }while(tp!=nod);
        sol.push_back(cctc);
    }
}