#include <fstream>
#include <vector>
#include <stack>
#define N 1000005
using namespace std;
ifstream fin ("ctc.in");
ofstream fout ("ctc.out");
vector <int> v1[N],v2[N],a[N];
stack <int> s;
int nr;
bool viz1[N],viz2[N];

void bfs1(int nod)
{
    viz1[nod]=1;
    for(int i=0;i<v1[nod].size();++i)
        if(viz1[v1[nod][i]]==0)
            bfs1(v1[nod][i]);
    s.push(nod);
}

void bfs2(int nod)
{
    viz2[nod]=1;
    for(int i=0;i<v2[nod].size();++i)
        if(viz2[v2[nod][i]]==0)
            bfs2(v2[nod][i]);
    a[nr].push_back(nod);
}

int main()
{
    int n,m,x,y;
    fin>>n>>m;
    for(int i=1;i<=m;++i)
        fin>>x>>y,v1[x].push_back(y),v2[y].push_back (x);
    for(int i=1;i<=n;++i)
        if(viz1[i]==0)
            bfs1(i);
    while(s.empty()==0)
    {
        if(viz2[s.top()]==0)
            ++nr,bfs2(s.top());
        s.pop();
    }
    fout<<nr<<'\n';
    for(int i=1;i<=nr;++i)
    {
        for(int j=0;j<a[i].size();++j)
            fout<<a[i][j]<< ' ';
        fout << '\n';
    }
    return 0;
}