#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f ("ctc.in");
ofstream g ("ctc.out");
int n,m;
vector<int>adiacenta[100001];
vector<int>adiacenta_comp[100001];
int comp;
int viz[100001];
vector<int> rasp[100001];
stack<int>st;
void DFS(int nod)
{
    viz[nod] = 1;
    for(auto x:adiacenta[nod])
    {
        if(viz[x] == 0)
        {
            DFS(x);
        }
    }
    st.push(nod);

}
void DFS_comp(int nod)
{
    rasp[comp].push_back(nod);
    viz[nod] = 2;
    for(auto x:adiacenta_comp[nod])
    {
        if(viz[x]!=2)
        {
            DFS_comp(x);
        }
    }

}
int main()
{
    f >> n >> m;
    for(int i = 1;i<=m;i++)
    {
        int x,y;
        f >>x >> y;
        adiacenta[x].push_back(y);
        adiacenta_comp[y].push_back(x);
    }
    for(int i = 1;i<=n;i++)
    {
        if(!viz[i])
            DFS(i);
    }
    while(!st.empty())
    {
        int curent = st.top();
        st.pop();
        if(viz[curent] == 1)
        {
            comp++;
            DFS_comp(curent);
        }
    }
    g << comp<<'\n';
    for(int i = 1;i<=comp;i++)
    {
        for(auto x:rasp[i])
            g << x<< " ";
        g << '\n';

    }
}