#include <bits/stdc++.h>
#define mod 1000000007
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
vector<int> v[100001];
vector<int> tr[100001];
stack<int> st;
bool viz[100001];
vector<int> ans[100001];
void dsf1(int nod, int cat)
{
    if (viz[nod] == 1)
        return;
    else
    {
        ans[cat].push_back(nod);
        viz[nod] = 1;
    }

    for (auto vecin : tr[nod])
        dsf1(vecin, cat);
}
void dfs(int nod)
{
    if (viz[nod] == 1)
        return;
    else
        viz[nod] = 1;
    for (auto vecin : v[nod])
        dfs(vecin);
    st.push(nod);
}
void solve()
{
    int n, m;
    in >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        int a, b;
        in >> a >> b;
        v[a].push_back(b);
        tr[b].push_back(a);
    }
    for (int i = 1; i <= n; ++i)
        if (viz[i] == 0)
            dfs(i);
    for (int i = 1; i <= n; ++i)
        viz[i] = 0;
    int place = 1;
    while (!st.empty())
    {
        int top = st.top();
        if (viz[top] == 0)
        {
            dsf1(top, place);
            place++;
        }
        st.pop();
    }
    out << place - 1 << '\n';
    for (int i = 1; i < place; ++i)
    {
        for (auto j : ans[i])
            out << j << ' ';
        out << '\n';
    }
}
main()
{
    int t = 1;
    //cin >> t;
    while (t--)
        solve();
}