#include <bits/stdc++.h>

using namespace std;

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

int n, m, viz[100041], q;
vector <int> v[100041];
vector <int> v_inv[100041];
vector <int> ctc[100041];
stack <int> s;

void read()
{
    fin >> n >> m;
    for (int i=0;i<m;++i)
    {
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);
        v_inv[y].push_back(x);
    }
}

void dfs(int x)
{
    viz[x]++;
    for(int i = 0; i < v[x].size(); i++)
        if(!viz[v[x][i]])
        {
            dfs(v[x][i]);
        }
    s.push(x);
}

void dfs2(int x)
{
    viz[x]++;
    ctc[q].push_back(x);
    for(int i = 0; i < v_inv[x].size(); i++){
        if(viz[v_inv[x][i]]==1)
        {
            dfs2(v_inv[x][i]);
        }
    }
}

int main()
{
    read();
    for (int i=1;i<=n;++i)
    {
        if (!viz[i])
            dfs(i);
    }
    while (!s.empty())
    {
        if(viz[s.top()]==1){
            dfs2(s.top());
            q++;
        }
        else
            s.pop();
    }
    fout << q << "\n";
    for (int i=0;i<q;++i){
        for (int j=0;j<ctc[i].size();++j)
            fout << ctc[i][j] << " ";
        fout << "\n";
    }
    return 0;
}