#include <bits/stdc++.h>
using namespace std;

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

int n, m;

vector<int> v[100005];
vector<int> t[100005];
vector<int> tout;
vector<int> comp[100005];

bool viz[100005];

int nr;

void dfs(int nod)
{
    viz[nod]=true;
    for(auto i : v[nod]){
        if(!viz[i]){
            dfs(i);
        }
    }
    tout.push_back(nod);
}

void dfs1(int nod)
{
    viz[nod]=true;
    for(int i : t[nod]){
        if(!viz[i])
            dfs1(i);
    }
    comp[nr].push_back(nod);
}

void solve()
{
    fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);
        t[y].push_back(x);
    }
    for(int i = 1; i <= n; ++i){
        if(!viz[i]){
            dfs(i);
        }
    }
    reverse(tout.begin(), tout.end());
    memset(viz, 0, sizeof(viz));
    for(int i : tout){
        if(!viz[i]){
            dfs1(i);
            nr++;
        }
    }
    fout << nr << '\n';
    for(int i = 0;  i < nr; ++i){
        for(int x : comp[i]){
            fout << x << " ";
        }
        fout << '\n';
    }
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    solve();
    return 0;
}