#include <bits/stdc++.h>

using namespace std;

unordered_map<int, vector<int>> graph;
int tc = 0;
stack<int> st;
vector<int> vis;
vector<int> dfn;
vector<int> low;
vector<int> cur;
map<int, set<int>> ans;

void tarjan(int u)
{
    low[u] = dfn[u] = ++tc;
    st.push(u);
    cur[u] = 1;
    for (auto x : graph[u])
    {
        if (!dfn[x])
        {
            // same as dfs
            tarjan(x);
            low[u] = min(low[u], low[x]);
        }
        else if (cur[x])
        {
            // in and searched, son
            low[u] = min(low[u], dfn[x]); // notice dfn
        }
    }
    if (low[u] == dfn[u])
    {
        // found strong!
        set<int> tmp;
        int t = 0x3f3f3f3f;
        int x;
        do
        {
            // pop all until u!
            x = st.top();
            st.pop();
            tmp.insert(x);
            cur[x] = 0;
            t = min(t, x);
        } while (x != u);
        ans[t] = tmp;
    }
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);
    int n, m;
    cin >> n >> m;
    vis.resize(n + 1), dfn.resize(n + 1), low.resize(n + 1), cur.resize(n + 1);
    for (int i = 1; i <= m; i++)
    {
        int u, v;
        cin >> u >> v;
        graph[u].push_back(v);
    }
    tarjan(1);
    cout << ans.size() << "\n";
    for (auto x : ans)
    {
        for (auto y : x.second)
        {
            cout << y << " ";
        }
        cout << "\n";
    }
    return 0;
}