#include <bits/stdc++.h>
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");

vector <int> L[200005];
vector <int> T[200005];
vector <int> cnt[200005];
int n, m, st[10005], top, viz[100005], ct;

void DFS(int k)
{
    viz[k] = 1;
    for(auto i : L[k])
        if(viz[i] == 0) DFS(i);
    st[++top] = k;
}
void SortTop()
{
    for(int i = 1; i <= n; i++)
        if(viz[i] == 0) DFS(i);
}
void ReInit()
{
    for(int i = 1; i <= n; i++)
        viz[i] = 0;
}
void DFS2(int k)
{
    viz[k] = ct;
    for(auto i : T[k])
        if(viz[i] == 0) DFS2(i);
    cnt[ct].push_back(k);
}
void CTC()
{
    for(int i = n; i >= 1; i--)
        if(viz[st[i]] == 0)
        {
            ct++;
            DFS2(st[i]);
        }

}
int main()
{
    int i, x, y;
    in >> n >> m;
    for(i = 1; i <= m; i++)
    {
        in >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
    SortTop();
    ReInit();
    CTC();
    out << ct << "\n";
    for(i = 1; i <= ct; i++)
    {
        for(auto j : cnt[i])
            out << j << " ";
        out << "\n";
    }
    return 0;
}