#include <fstream>
#include <stack>
#include <vector>
using namespace std;
ifstream cin("ctc.in");
ofstream cout("ctc.out");
const int MAXN = 100005;
#define Min(a, b)  ((a) < (b) ? (a) : (b))
vector < int > adj[MAXN], d, low, in_stack, C[MAXN];
stack < int > S;
int ordine, n, con;

void Citire()
{
    int m, x, y;
    cin >> n >> m;
    while( m ) cin >> x >> y, adj[x].push_back(y), -- m;
}

void Afisare()
{
    cout << con << "\n";
    for (int i = 0; i < con; ++ i)
    {
        for (int j = 0; j < C[i].size(); ++ j) cout << C[i][j] << ' ';
        cout << '\n';
    }
}



void Tarjan(int n)
{
    d[n] = low[n] = ordine++;
    S.push(n), in_stack[n] = 1;
    int v;
    for (int i = 0; i < adj[n].size(); ++ i)
    {
        v = adj[n][i];
        if (d[v] == -1) Tarjan(v), low[n] = Min(low[n], low[v]);
        else if (in_stack[v]) low[n] = Min(low[n], low[v]);
    }
    if (d[n] == low[n]) {
        int node;
        do {
            node = S.top();
            C[con].push_back(node);
            S.pop(), in_stack[node] = 0;
        }
        while (node != n);
        con++;
    }
}

void SCC()
{
    d.resize(n + 1), low.resize(n + 1), in_stack.resize(n + 1);
    d.assign(n + 1, -1), in_stack.assign(n + 1, 0);
    for (int i = 1; i <= n; ++ i) if (d[i] == -1) Tarjan(i);
}

int main()
{
    Citire();
    SCC();
    Afisare();
}