#include <fstream>
#include <climits>
#include <vector>

using namespace std;

ifstream cin("ctc.in");
ofstream cout("ctc.out");

const int NMAX = 1e5;
int n, m;
vector<int> G[NMAX + 1], GT[NMAX + 1];
int Nodes[NMAX + 1], ind;
bool vizG[NMAX + 1], vizGT[NMAX + 1];
vector<int> CTC[NMAX + 1];
int nr_ctc;

void DFSG(int k)
{
    vizG[k] = 1;
    for(int Node : G[k])
        if(!vizG[Node])
            DFSG(Node);
    Nodes[++ind] = k;
}

void DFSGT(int k)
{
    vizGT[k] = 1;
    for(int Node : GT[k])
        if(!vizGT[Node])
            DFSGT(Node);
    CTC[nr_ctc].push_back(k);
}

int main()
{
    cin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        cin >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }

    for(int i = 1; i <= n; i++)
        if(!vizG[i])
            DFSG(i);

    for(int i = ind; i >= 1; i--)
        if(!vizGT[Nodes[i]])
            nr_ctc++, DFSGT(Nodes[i]);

    cout << nr_ctc << '\n';
    for(int i = 1; i <= nr_ctc; i++, cout << '\n')       
        for(int x : CTC[i])
            cout << x << ' ';
            
    return 0;
}