#include<fstream>
#include<vector>
#include<stack>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector<vector<int>>G;
vector<vector<int>>CC;
vector<int>C;
stack<int>S;
int L[100001],niv[100001];
bool InS[100001];
int n,m,nv;
void Citire()
{
    fin>>n>>m;
    G.resize(n+1);
    for(int i=1;i<=m;i++)
    {
        int x,y;
        fin>>x>>y;
        G[x].push_back(y);
    }
}
void Afisare()
{
    fout<<CC.size()<<'\n';
    for(auto V : CC)
    {
        for(auto x : V)
            fout<<x<<" ";
        fout<<'\n';
    }
}
void Tarjan(int x)
{
    nv++;
    L[x]=nv;
    niv[x]=nv;
    S.push(x);
    InS[x]=true;
    for(auto y : G[x])
    {
        if(niv[y]==0)
        {
            Tarjan(y);
            L[x]=min(L[x],L[y]);
        }
        else
        {
            if(InS[y])
                L[x]=min(L[x],niv[y]);
        }
    }
    if(L[x]==niv[x])
    {
        C.clear();
        int y=-1;
        while(x!=y)
        {
            y=S.top();
            InS[y]=false;
            C.push_back(y);
            S.pop();
        }
        CC.push_back(C);
    }
}
int main()
{
    Citire();
    for(int i=1;i<=n;i++)
        if(!niv[i])
            nv=0,Tarjan(i);
    Afisare();
}