#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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


const int N=100005;

vector<int>suc[N];
vector<int>pred[N];
vector<int>strt;
bool viz[N];
int n, m;
int k;
vector<int> ctc[N];


void dfs_sortaret(int x)
{
    viz[x]=1;
    for(auto y: suc[x])
    {
        if(!viz[y])
            dfs_sortaret(y);
    }
    strt.push_back(x);
}

void dfs_ctc(int x)
{
    ctc[k].push_back(x);
    viz[x]=0;
    for(auto y: pred[x])
    {
        if(viz[y])
        {
            dfs_ctc(y);
        }
    }
}

int main()
{
    int x, y, m;
    in>>n>>m;
    for(int i=1; i<=m; i++)
    {
        in>>x>>y;
        suc[x].push_back(y);
        pred[y].push_back(x);
    }
    for(int i=1; i<=n; i++)
    {
        if(!viz[i])
        {
            dfs_sortaret(i);
        }
    }

    for(int i=n-1; i>=0; i--)
    {
        if(viz[strt[i]])
        {
            k++;
            dfs_ctc(strt[i]);
        }
    }
    out<<k<<'\n';
    for(int i=1; i<=k; i++)
    {
        for(auto j:ctc[i])
            out<<j<<' ';
        out<<'\n';
    }
    return 0;
}