#include <bits/stdc++.h>

using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
void dfs(int nod, const vector<vector<int>>& v, vector<bool>& viz, vector<int>& sor)
{
    viz[nod]=true;
    for(auto it : v[nod])
        if(!viz[it])
            dfs(it,v,viz,sor);
    sor.push_back(nod);
}
int main()
{
    int n,m,a,b;
    in>>n>>m;
    vector<vector<int>> v(n+5);
    vector<vector<int>> inv(n+5);
    vector<vector<int>> ctc;
    vector<int> sor;
    vector<bool> viz(n+5);
    for(int i=1;i<=m;i++)
    {
        in>>a>>b;
        v[a].push_back(b);
        inv[b].push_back(a);
    }
    for(int i=1;i<=n;i++)
        if(!viz[i])
            dfs(i,v,viz,sor);
    reverse(sor.begin(),sor.end());
    viz=vector<bool>(n+5);
    for(auto i:sor)
        if(!viz[i])
        {
            ctc.push_back(vector<int>());
            dfs(i,inv,viz,ctc.back());
        }
    out<<ctc.size()<<"\n";
    for(auto it1:ctc)
    {
        for(auto it2:it1)
            out<<it2<<" ";
        out<<"\n";
    }
    return 0;
}