#include <iostream>
#include <fstream>
#include <vector>

#define nmax 100001

using namespace std;

int n, m, numComp;
int i, j, x, y;
bool vizG[nmax], vizGT[nmax];
vector <int> G[nmax], GT[nmax];
vector <int> sol[nmax];

int postordine[nmax];

void dfsG(int nod)
{
    vizG[nod] = true;
    for (int i = 0; i < G[nod].size(); i++)
        if (!vizG[G[nod][i]])
            dfsG(G[nod][i]);
    postordine[ ++postordine[0] ] = nod;
}

void dfsGT(int nod)
{
    vizGT[nod] = true;
    sol[numComp].push_back(nod);
    for (int i = 0; i < GT[nod].size(); i++)
        if (!vizGT[GT[nod][i]])
            dfsGT(GT[nod][i]);
}

int main()
{
    
    ifstream fi("ctc.in");
    ofstream fo("ctc.out");
    
    fi >> n >> m;
    
    for (i = 1; i <= m; i++)
    {
        fi >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    
    for (i = 1; i <= n; i++)
        if (!vizG[i])
            dfsG(i);
    
    for (i = postordine[0]; i > 0; i--)
    {
        int currNode = postordine[i];
        
        if (!vizGT[currNode])
        {
            numComp++;
            dfsGT(currNode);
        }
        
    }
    
    fo << numComp << "\n";
    for (i = 1; i <= numComp; i++)
    {
        for (j = 0; j < sol[i].size(); j++)
            fo << sol[i][j] << " ";
        fo << "\n";
    }
    
    fi.close();
    fo.close();
    
    return 0;
}