#include <bits/stdc++.h>
#define N 100001
#define M 200001
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
int nr,vf[2*M],urm[2*M],lst[N],v[N],k,a[N];
bool viz[2*M];
vector<int> c[N];
void dfs(int x)
{
    int p=lst[x],y;
    viz[x]=1;
    while(p)
    {
        y=vf[p];
        if(!viz[y])
            dfs(y);
        p=urm[p];
    }
    v[k++]=x;
}
void dfs1(int x,int root)
{
    int p=lst[x],y;
    viz[x]=0;
    c[a[root]].push_back(x);
    while(p)
    {
        y=vf[p];
        if(viz[y])
            dfs1(y,root);
        p=urm[p];
    }
}
void ad(int x,int y)
{
	vf[++nr]=y;
	urm[nr]=lst[x];
	lst[x]=nr;
}
int main()
{
    int n,m,i,x,y,l=0;
    in>>n>>m;
    for(i=1;i<=m;i++)
    {
        in>>x>>y;
        ad(x,y);
    }
    for(i=1;i<=n;i++)
        if(!viz[i])
            dfs(i);
    for(i=0;i<n;i++)
        if(viz[v[i]])
        {
            a[i]=l++;
            dfs1(v[i],i);
        }
    out<<l<<"\n";
    for(i=0;i<l;i++)
    {
        for(x=0;x<c[i].size();x++)
            out<<c[i][x]<<" ";
        out<<"\n";
    }
    return 0;
}