#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define buff ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr)
#define ll long long
#define int ll
const int N = 2e5 + 7;

std::set<std::pair<int, int>> E;

struct EBCC
{
    int n;
    std::vector<std::vector<int>> adj;
    std::vector<int> stk;
    std::vector<int> dfn, low, bel;
    int cur, cnt;

    EBCC()
    {
    }

    EBCC(int n)
    {
        init(n);
    }

    void init(int n)
    {
        this->n = n;
        adj.assign(n, {});
        dfn.assign(n, -1);
        low.resize(n);
        bel.assign(n, -1);
        stk.clear();
        cur = cnt = 0;
    }

    void addEdge(int u, int v)
    {
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    void dfs(int x, int p)
    {
        dfn[x] = low[x] = cur++;
        stk.push_back(x);

        for (auto y: adj[x])
        {
            if (y == p)
            {
                continue;
            }
            if (dfn[y] == -1)
            {
                E.emplace(min(x, y), max(x, y));
                dfs(y, x);
                low[x] = std::min(low[x], low[y]);
            }
            else if (bel[y] == -1 && dfn[y] < dfn[x])
            {
                E.emplace(min(x, y), max(x, y));
                low[x] = std::min(low[x], dfn[y]);
            }
        }

        if (dfn[x] == low[x])
        {
            int y;
            do
            {
                y = stk.back();
                bel[y] = cnt;
                stk.pop_back();
            } while (y != x);
            cnt++;
        }
    }

    std::vector<int> work()
    {
        for (int i = 0; i < n; ++i)
        {
            if (dfn[i] == -1)
            {
                dfs(i, -1);
            }
        }
        return bel;
    }

    struct Graph
    {
        int n;
        std::vector<std::pair<int, int>> edges;
        std::vector<int> siz;
        std::vector<int> cnte;
    };

    Graph compress()
    {
        Graph g;
        g.n = cnt;
        g.siz.resize(cnt);
        g.cnte.resize(cnt);
        for (int i = 0; i < n; i++)
        {
            g.siz[bel[i]]++;
            for (auto j: adj[i])
            {
                if (bel[i] < bel[j])
                {
                    g.edges.emplace_back(bel[i], bel[j]);
                }
                else if (bel[i] == bel[j] && i < j)
                {
                    g.cnte[bel[i]]++;
                }
            }
        }
        return g;
    }
};

void solve()
{
    int n, m;
    cin >> n >> m;
    EBCC ebcc(n);
    for (int i = 1; i <= m; ++i)
    {
        int f, t;
        cin >> f >> t;
        if (f == t)
        {
            continue;
        }
        ebcc.addEdge(f - 1, t - 1);
    }
    ebcc.work();
    vector<vector<int>> ans(ebcc.cnt);
    for (int i = 0; i < n; ++i)
    {
        ans[ebcc.bel[i]].push_back(i);
    }
    cout << ebcc.cnt << endl;
    for (const auto &x: ans)
    {
        cout << x.size();
        for (int u: x)
        {
            cout << ' ' << u + 1;
        }
        cout << endl;
    }
}

signed main()
{
    buff;
    int tt = 1;
    // cin >> tt;
    while (tt--)
    {
        solve();
    }
    return 0;
}