#include <bits/stdc++.h>
#define N 100001
using namespace std;

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



int n, m, q;
int k, DUD[N + 5];
bool viz[N];
vector <int> V1[N];
vector <int> V2[N];
vector <int> ctc[N];

void DFS1(int nod)
{
    viz[nod] = 1;

    for(auto it : V1[nod])
        if(!viz[it])
            DFS1(it);

    DUD[++k] = nod;
}

void DFS2(int nod)
{
    viz[nod] = 0;
    ctc[q].push_back(nod);

    for(auto it : V2[nod])
        if(viz[it] == 1)
            DFS2(it);
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++) {

        int x, y;
        fin >> x >> y;
        V1[x].push_back(y);
        V2[y].push_back(x);

    }

    for(int i = 1; i <= n; i++)
        if(!viz[i])
            DFS1(i);

    for(int i = n; i >= 1; i--)
        if(viz[DUD[i]] == 1)
            {
                q++;
                DFS2(DUD[i]);
            }

    fout << q << '\n';
    for(int i = 1; i <= q; i++)
    {
        for(auto it : ctc[i])
            fout << it << ' ';
        fout << '\n';
    }

    return 0;
}