#include <cstdio>
#include <vector>
#include <stack>
#include <algorithm>

using namespace std;

stack<int> st;
vector<int> g[100002];
vector<int> sol[100002];
int nr_sol = 0;
int counter = 0;
int index[100002], lowlink[100002];
bool in_stack[100002];

void scc(int node)
{
    index[node] = ++counter;
    lowlink[node] = counter;
    st.push(node);
    in_stack[node] = true;

    for (unsigned i = 0; i < g[node].size(); i++)
    {
        if (index[g[node][i]] == 0)
        {
            scc(g[node][i]);
            lowlink[node] = min(lowlink[node], lowlink[g[node][i]]);
        }
        else if (in_stack[g[node][i]])
            lowlink[node] = min(lowlink[node], index[g[node][i]]);
    }

    if (index[node] == lowlink[node])
    {
        ++nr_sol;
        while (1)
        {
            int w = st.top();
            st.pop();
            in_stack[w] = false;
            sol[nr_sol].push_back(w);
            if (w == node)
                break;
        }
    }
}

int main()
{
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);

    int n, m;
    scanf("%d%d", &n, &m);
    for (int i = 1, x, y; i <= m; i++)
    {
        scanf("%d%d", &x, &y);
        g[x].push_back(y);
    }

    for (int i = 1; i <= n; i++)
        if (index[i] == 0)
            scc(i);

    printf("%d\n", nr_sol);
    for (int i = 1; i <= nr_sol; i++)
    {
        for (unsigned j = 0; j < sol[i].size(); j++)
            printf("%d ", sol[i][j]);
        printf("\n");
    }


    return 0;
}