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

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

vector <int> a[100005], ctc[100005];
int n , m, id[100005], st[100005], top;
int onStack[100005], lowlink[100005], nr;
int nrctc; /// nr de componentele tari conexe
/// ctc[] - componentele tari conexe
void DFS_Tarj(int x)
{
    st[++top] = x;
    onStack[x] = 1;
    id[x] = lowlink[x] = ++nr;

    for(auto w : a[x])
    {
        if(id[w] == 0) DFS_Tarj(w);
        if(onStack[w] == 1)
            lowlink[x] = min(lowlink[w], lowlink[x]);
    }

    if(id[x] == lowlink[x])
    {
        nrctc++;
        ctc[nrctc].push_back(x);
        while(top > 0 and st[top] != x)
        {
            ctc[nrctc].push_back(st[top]);
            onStack[st[top]] = 0;
            lowlink[st[top]] = lowlink[x];
            top--;
        }
        onStack[st[top]] = 0;
        lowlink[st[top]] = lowlink[x];
        top--;
    }
}
int main()
{
    int x, y, i;
    in >> n >> m;
    for(i = 1; i <= m; i++)
    {
        in >> x >> y;
        a[x].push_back(y);
    }

    for(i = 1; i <= n; i++)
        if(id[i] == 0) DFS_Tarj(i);

    out << nrctc << "\n";
    for(i = 1; i <= nrctc; i++)
    {
        for(auto w : ctc[i])
            out << w << " ";
        out << "\n";
    }
    return 0;
}