#include <bits/stdc++.h>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");
const int MAXN = 100005;

bool inSt[MAXN];
int ll[MAXN], mark[MAXN], n, m, val, nr;
vector<int> graph[MAXN], comp[MAXN];
stack<int> st;

void read()
{
    fin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int x, y;
        fin >> x >> y;
        graph[x].push_back(y);
    }
}

void tarjan(int node)
{
    st.push(node);
    inSt[node] = true;
    mark[node] = ll[node] = ++val;
    for (const auto& it: graph[node])
        if (mark[it] == 0) {
            tarjan(it);
            ll[node] = min(ll[node], ll[it]);
        }
        else if (inSt[it] == true)
            ll[node] = min(ll[node], mark[it]);
    if (ll[node] == mark[node]) {
        while (!st.empty()) {
            int top = st.top();
            st.pop();
            inSt[top] = false;
            comp[nr].push_back(top);
            if (top == node)
                break;
        }
        ++nr;
    }
}

void print()
{
    fout << nr << '\n';
    for (int i = 0; i < nr; ++i) {
        for (const auto &it: comp[i])
            fout << it << ' ';
        fout << '\n';
    }
}

int main()
{
    read();
    for (int i = 1; i <= n; ++i)
        if (mark[i] == 0)
            tarjan(i);
    print();
    return 0;
}