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

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

/*
*/
#define cin fin
#define cout fout


const int NMAX=1e5+10;
const int MMAX=2e5+10;

int n, m, x, y, k, kscc;
vector<int>sccs[NMAX];
vector<int>rel[NMAX];
vector<int>Stack;
int instack[NMAX];
int index[NMAX];


void read()
{
    cin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        cin>>x>>y;
        rel[x].push_back(y);
    }
}


void scc(int nod)///strongly connected components
{
    Stack.push_back(nod);
    instack[nod]=1;
    index[nod]=++k;
    int indexStart=k;
    for(auto el:rel[nod])
    {
        if(!index[el])
            scc(el);
        if(instack[el])
            index[nod]=min(index[nod], index[el]);
    }
    if(index[nod]==indexStart)
    {
        kscc++;
        while(!Stack.empty())
        {
            int aux=Stack.back();
            Stack.pop_back();
            instack[aux]=0;
            sccs[kscc].push_back(aux);
            if(aux==nod)
                break;
        }
    }
}

void solve()
{
    for(int i=1; i<=n; i++)
        if(!index[i])
            scc(i);
    cout<<kscc<<"\n";
    for(int i=1; i<=kscc; i++)
    {
        for(auto el:sccs[i])
            cout<<el<<" ";
        cout<<"\n";
    }
}


int main()
{
    read();
    solve();

    return 0;
}