#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#define NMAX 100000

using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");

int cnt, nrctc, n, m, mini[NMAX+10], idx[NMAX+10], inStack[NMAX+10];
stack <int> stiva;
vector <int> nod[NMAX+10], ctc[NMAX+10];

void dfs(int x)
{   cnt++;
    mini[x] = idx[x] = cnt;
    stiva.push(x);
    inStack[x] = 1;
    for(int i=0; i<nod[x].size(); i++)
        {   if(!idx[nod[x][i]])
                {   dfs(nod[x][i]);
                    mini[x] = min(mini[x], mini[nod[x][i]]);
                }
            else if(inStack[nod[x][i]])
                mini[x] = min(mini[x], mini[nod[x][i]]);
        }
    if(idx[x] == mini[x])
        {   nrctc++;
            while(stiva.top() != x)
                {   ctc[nrctc].push_back(stiva.top());
                    stiva.pop();
                    inStack[stiva.top()] = 0;
                }
            ctc[nrctc].push_back(x);
            inStack[x] = 0;
            stiva.pop();
        }
}

int main()
{
    f >> n >> m;
    for(int i=1; i<=m; i++)
        {   int nod1, nod2;
            f >> nod1 >> nod2;
            nod[nod1].push_back(nod2);
        }
    for(int i=1; i<=n; i++)
        if(!idx[i]) dfs(i);
    g << nrctc << '\n';
    for(int i=1; i<=nrctc; i++)
        {   for(int j=0; j<ctc[i].size(); j++) g << ctc[i][j] << ' ';
            g << '\n';
        }
    return 0;
}