#include <bits/stdc++.h>
#define Nmax 100005
using namespace std;
ifstream fin ("ctc.in");
ofstream fout ("ctc.out");

vector <int> v[Nmax], vt[Nmax], c[Nmax];
int viz[Nmax], a[Nmax], k, n, m;

void dfs1(int x)
{
    viz[x]=1;
    for(auto it:v[x])
        if(viz[it]==0)
            dfs1(it);
    a[++k]=x;
}
void dfs2(int x)
{
    viz[x]=1;
    for(auto it:vt[x])
        if(viz[it]==0)
            dfs2(it);
    c[k].push_back(x);
}
int main()
{
    fin >> n >> m;
    for(int i=1;i<=m;i++)
        {
            int x, y;
            fin >> x >> y;
            v[x].push_back(y);
            vt[y].push_back(x);
        }
    for(int i=1;i<=n;i++)
        if(!viz[i])
            dfs1(i);
    memset(viz, 0, sizeof(viz));
    k=0;
    for(int i=n;i>=1;i--)
        if(!viz[a[i]])
        {
            k++;
            dfs2(a[i]);
        }
    fout << k << '\n';
    for(int i=1;i<=k;i++)
    {
        for(auto it:c[i])
            fout << it << ' ';
        fout << '\n';
    }
    return 0;
}