#include <bits/stdc++.h>
using namespace std;
ifstream f ("ctc.in");
ofstream g ("ctc.out");
const int nmax=1e5+3;
int n,m,a,b,viz[nmax],p,k,act,va[nmax],nod;
vector <int> v[nmax],vt[nmax],sol[nmax];
stack <int> st;
void dfs1(int nod)
{
    viz[nod]=1;
    for(int i=0;i<v[nod].size();++i)
    {
        if(viz[v[nod][i]]) continue;
        dfs1(v[nod][i]);
    }
    st.push(nod);
}
void dfs2(int nod)
{
    va[nod]=p;
    for(int i=0;i<vt[nod].size();++i)
    {
        if(va[vt[nod][i]]) continue;
        dfs2(vt[nod][i]);
    }
    sol[p].push_back(nod);
}
int main()
{
    f>>n>>m;
    while(m--)
    {
        f>>a>>b;
        v[a].push_back(b);
        vt[b].push_back(a);
    }
    for(int i=1;i<=n;++i) if(!viz[i]) dfs1(i);
    while(!st.empty())
    {
        nod=st.top();
        st.pop();
        if(va[nod]) continue;
        ++p;
        act=viz[nod];
        dfs2(nod);
    }
    g<<p<<'\n';
    for(int i=1;i<=p;++i)
    {
        for(int j=0;j<sol[i].size();++j) g<<sol[i][j]<<' ';
        g<<'\n';
    }
    return 0;
}