#include <fstream>
#include <vector>
#include <bitset>
#include <algorithm>
#include <deque>
using namespace std;
#define N 100004
int n,k,r,e[N],l[N];
vector <int> v[N],s[N];
deque <int> q;
bitset <N> u;

void tarjan(int x)
{
    e[x]=++k;
    l[x]=k;
    q.push_back(x);
    u[x]=1;
    for(int i=0;i<v[x].size();i++)
    {
        if(!e[v[x][i]])
        {
            tarjan(v[x][i]);
            l[x]=min(l[x],l[v[x][i]]);
        }
        else if(u[v[x][i]])
            l[x]=min(l[x],l[v[x][i]]);
    }
    if(e[x]==l[x]&&!q.empty())
    {
        do{
            u[q.back()]=0;
            s[r].push_back(q.back());
            q.pop_back();
        }while(!q.empty()&&q.back()!=x);
        r++;
    }
}

int main()
{
    ifstream in("ctc.in");
    ofstream out("ctc.out");
    int m,i,j,x,y;
    in>>n>>m;
    while(m--)
    {
        in>>x>>y;
        v[x].push_back(y);
    }
    for(i=1;i<=n;++i)
        if(!e[i])
            tarjan(i);
    out<<r<<'\n';
    for(i=0;i<r;i++)
    {
        for(j=0;j<s[i].size();j++)
            out<<s[i][j]<<' ';
        out<<'\n';
    }
    return 0;
}