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

ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int Inf = 0x3f3f3f3f;

int n, m;
int nv;
vector<vector<int> > G, C;
vector<int> niv, L, c;
vector<bool> inS;
stack<int> st;

void Read();
void Tarjan(int nod);

int main()
{
    Read();

    for ( int i = 1; i <= n; ++i )
        if ( niv[i] == 0 )
            nv = 0, Tarjan(i);

    fout << C.size() << "\n";

	for (const auto& c : C)
    {
		for (const auto& x : c)
			fout << x << ' ';
		fout << '\n';
	}
    fin.close();
    fout.close();
    return 0;
}

void Read()
{

    fin >> n >> m;
    int x, y;
    G = vector<vector<int>>(n + 1);
    niv = L = vector<int>(n + 1);
    inS = vector<bool>(n + 1);
    for ( int i = 1; i <= m; ++i )
    {
        fin >> x >> y;
        G[x].push_back(y);
    }
}

void Tarjan(int x)
{
    niv[x] = L[x] = ++nv;
    st.push(x);
    inS[x] = true;

    for ( const auto& y : G[x] )
        if ( niv[y] == 0 )
        {
            Tarjan(y);
            L[x] = min(L[x], L[y]);
        }
        else
            if ( inS[y] )
                L[x] = min(L[x], niv[y]);


    if ( niv[x] == L[x] )
    {
        c.clear();
        int x2;
        while ( true )
        {
            c.push_back(x2 = st.top());
            st.pop();
            inS[x2] = false;
            if ( x2 == x )
				break;
        }
        C.push_back(c);
    }
}