#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#include <string.h>
#define N 100001

using namespace std;

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

vector<int> graph[N];
vector<int> rev_graph[N];
int n;
stack<int> top;
bool vis[N];
int nrcomp;
vector<int> ans[N];

void dfs1(int x)
{
    for(auto y: rev_graph[x])
    {
        if(!vis[y])
        {
            vis[y]=1;
            dfs1(y);
        }
    }
    top.push(x);
}

void dfs2(int x)
{
    for(auto y: graph[x])
    {
        if(!vis[y])
        {
            vis[y]=1;
            dfs2(y);
        }
    }
    ans[nrcomp].push_back(x);
}

int main()
{
    int m;
    in >> n >> m;
    for(int i=0;i<m;i++)
    {
        int x,y;
        in >> x >> y;
        graph[x].push_back(y);
        rev_graph[y].push_back(x);
    }
    for(int i=1;i<=n;i++)
    {
        if(!vis[i])
        {
            vis[i]=1;
            dfs1(i);
        }
    }
    memset(vis, 0, sizeof(vis));
    while(!top.empty())
    {
        int x=top.top();
        top.pop();
        if(!vis[x])
        {
            nrcomp++;
            vis[x]=1;
            dfs2(x);
        }
    }
    out << nrcomp << "\n";
    for(int i=1;i<=nrcomp;i++)
    {
        for(auto y:ans[i])
        {
            out << y << " ";
        }
        out << "\n";
    }
    return 0;
}