#include <bits/stdc++.h>
#define NMAX 100010
using namespace std;

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

int n, m, x, y, cate;
vector <int> G[NMAX], inv[NMAX],sol[NMAX];
bitset <NMAX> viz, viz2;
stack <int> Q;

void DFS(int nod)
{
    viz[nod] = 1;
    for(int i = 0; i < G[nod].size(); ++i)
    {
        int vecin = G[nod][i];
        if(!viz[vecin])
            DFS(vecin);
    }
    Q.push(nod);
}
void DFS2(int nod)
{
    viz2[nod] = 1;
    sol[cate].push_back(nod);
    for(int i = 0; i < inv[nod].size(); ++i)
    {
        int vecin = inv[nod][i];
        if(!viz2[vecin])
            DFS2(vecin);
    }
}
int main()
{
    f >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        f >> x >> y;
        G[x].push_back(y);
        inv[y].push_back(x);
    }
    for(int i = 1; i <= n; ++i)
        if(!viz[i])
            DFS(i);
    while(!Q.empty())
    {
        int nod = Q.top();
        Q.pop();
        if(!viz2[nod])
        {
            cate++;
            DFS2(nod);
        }
    }
    g << cate << '\n';
    for(int i = 1; i <= cate; ++i, g << '\n')
        for(int j = 0; j < sol[i].size(); ++j)
            g << sol[i][j] << ' ';
    f.close();
    g.close();
    return 0;
}