#include <fstream>
#include <stack>
#include <vector>

using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
const int N=100005;
int n,m,id,nrctc,index[N],lowlink[N];//index tine minte vizitati+nr de ordine al efectuarii dfs
bool inside[N];
vector<int>a[N],sol[N];
stack<int>stiva;

void dfs(int x)
{
    int y;
    index[x]=lowlink[x]=++id;
    stiva.push(x);
    inside[x]=true;
    for(unsigned i=0;i<a[x].size();i++)
    {
        y=a[x][i];
        if(index[y]==0)
            dfs(y);
        if(inside[y])
            lowlink[x]=min(lowlink[x],lowlink[y]);
    }
    int varf;
    if(index[x]==lowlink[x])
    {
        nrctc++;
        do
        {
            varf=stiva.top();
            sol[nrctc].push_back(varf);
            inside[varf]=false;
            lowlink[varf]=index[x];
            stiva.pop();
        }while(varf!=x);
    }
}

int main()
{
    int x,y;
    in>>n>>m;
    for(int i=1;i<=m;i++)
    {
        in>>x>>y;
        a[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
        if(index[i]==0)
            dfs(i);
    out<<nrctc<<'\n';
    for(int i=1;i<=nrctc;i++)
    {
        for(unsigned j=0;j<sol[i].size();j++)
            out<<sol[i][j]<<' ';
        out<<'\n';
    }
    return 0;
}