#include <fstream>
#include <vector>
#include <bitset>
#include <stack>
using namespace std;

#define SZ 100003
#define INF 1<<27

ifstream is ("ctc.in");
ofstream os ("ctc.out");

int N, M, Index[SZ], L[SZ], idx;
bitset<SZ> B;
vector <int> G[SZ], C;
vector < vector <int> > SCC;
stack <int> S;

void Tarjan(int x);

int main()
{
    is >> N >> M;
    for (int i = 1; i <= N; ++i)
        Index[i] = INF;
    for (int i = 1, a, b; i <= M; ++i)
    {
        is >> a >> b;
        G[a].push_back(b);
    }
    for (int i = 1; i <= N; ++i)
        if (Index[i] == INF)
            Tarjan(i);
    os << SCC.size() << '\n';
    for (int i = 0; i < SCC.size(); ++i)
    {
        for (int j = 0; j < SCC[i].size(); ++j)
            os << SCC[i][j] << ' ';
        os << '\n';
    }

    is.close();
    os.close();
}

void Tarjan(int x)
{
    Index[x] = L[x] = idx++;
    S.push(x);
    B[x] = 1;
    int node;
    for (int j = 0; j < G[x].size(); ++j)
    {
        node = G[x][j];
        if (Index[node] == INF)
        {
            Tarjan(node);
            L[x] = min(L[x], L[node]);
        }
        else
            if (B[node] == 1)
                L[x] = min(L[x], L[node]);
    }
    if (L[x] == Index[x])
    {
        do
        {
            node = S.top(), S.pop();
            C.push_back(node);
            B[node] = 0;
        }
        while (node != x);
        SCC.push_back(C);
        C.clear();
    }
};