#include <fstream>
#include <stack>
#include <vector>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n, m, i, j, nr, niv[100010], low[100010], viz[100010], t, aux, x, y;

vector<int> l[100010], c[100010];
stack<int> st;

void dfs(int x){
    t++;
    niv[x]=low[x]=t;
    st.push(x);
    viz[x]=1;
    for(int i=0; i<l[x].size(); i++)
    {
        if(viz[ l[x][i] ]==0){
            dfs(l[x][i]);
            low[x]=min(low[x], low[ l[x][i] ]);
       }
       else
           low[x]=min(low[x], niv[ l[x][i] ]);
    }
    if(niv[x]==low[x])
    {
        nr++;
        do
        {
            aux=st.top();
            c[nr].push_back(aux);
            st.pop();
        }while(x!=aux);
    }
}

int main(){
    f>>n>>m;
    for(i=1; i<=m; i++)
    {
        f>>x>>y;
        l[x].push_back(y);
    }
    for(i=1; i<=n; i++)
        if(viz[i]==0)
            dfs(i);
    g<<nr<<"\n";
    for(i=1; i<=nr; i++)
    {
        for(j=0; j<c[i].size(); j++)
            g<<c[i][j]<<' ';
        g<<"\n";
    }
    return 0;
}