#include <bits/stdc++.h>

#define NMAX 100000
#define ll long long
#define MOD 666013
using namespace std;

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

int n,m;
vector<int> adj[NMAX+1];
vector<int> inv[NMAX+1];
vector<int> res[NMAX+1];

int ctc[NMAX+1];
stack<int> S;
bool v[NMAX+1];

int k=0;

void dfs1(int node)
{
    v[node]=1;
    for(int i : adj[node])
    {
        if(!v[i])
        {
            dfs1(i);
        }
    }
    S.push(node);
}
void dfs2(int node)
{
    ctc[node]=k;
    for(int i : inv[node])
    {
        if(!ctc[i])
        {
            dfs2(i);
        }
    }
}
int main()
{
    fin >> n >> m;
    for(int i=1;i<=m;i++)
    {
        int a,b;
        fin >> a >> b;
        adj[a].push_back(b);
        inv[b].push_back(a);
    }
    for(int i=1;i<=n;i++)
    {
        if(!v[i])
        {
            dfs1(i);
        }
    }
    while(!S.empty())
    {
        if(!ctc[S.top()])
        {
            ++k;
            dfs2(S.top());
        }
        S.pop();
    }
    for(int i=1;i<=n;i++)
    {
        res[ctc[i]].push_back(i);
    }
    fout << k << "\n";
    for(int i=1;i<=k;i++)
    {
        for(int j : res[i])
        {
            fout << j << " ";
        }
        fout << "\n";
    }

}