#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;
int n,m,i,j,x,y,t,k,nr,d[100005],low[100005],st[100005];
bool viz[100005];

vector <int> v[100005],sol[100005];

void dfs(int nod)
{
    t++;
    d[nod]=low[nod]=t;
    st[++k]=nod;
    viz[nod]=1;
    for (int i=0; i<v[nod].size(); i++)
        if (d[v[nod][i]]==0)
         {
               dfs(v[nod][i]);
                low[nod]=min(low[nod],low[v[nod][i]]);
           }
         else
            if(viz[v[nod][i]]==1)
              low[nod]=min(low[nod],d[v[nod][i]]);
    if(low[nod]==d[nod]){
        nr++;
        do{
            x=st[k--];
            viz[x]=0;
            sol[nr].push_back(x);
        }while(x!=nod&&k>0);

        }

    }


int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&n,&m);
    for (i=1; i<=m; i++)
    {
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
    }
    for(i=1;i<=n;i++)
        if(d[i]==0)
            dfs(i);
printf("%d\n",nr);
    for (i=1; i<=nr; i++)
    {
        for (j=0; j<sol[i].size(); j++)
            printf("%d ",sol[i][j]);
        printf("\n");
    }
    return 0;
}