#include<bits/stdc++.h>
#define maxN 100005
using namespace std;

int ctc,low[maxN],niv[maxN];
vector<int> c[maxN];
int st[maxN],vf;
vector<int> v[maxN];
bool inStack[maxN];
inline void dfs(int nod)
{
    //low[nod]=niv[nod]=lvl;
    st[++vf]=nod;
    low[nod]=niv[nod]=vf;
    inStack[nod]=1;
    for(vector<int>::iterator it=v[nod].begin();it!=v[nod].end();it++)
    {
        if(!niv[*it])
        {
            dfs(*it);
            low[nod]=min(low[nod],low[*it]);
        }
            else
        if(inStack[*it])
        {
            low[nod]=min(low[nod],low[*it]);
        }
    }

    if(low[nod]==niv[nod])
    {
        ctc++;
        int x;
        do
        {
            x=st[vf];
            //printf("%d\n",x);
            c[ctc].push_back(x);
            vf--;
        }while(vf && x!=nod);
    }
}
int n,m,x,y;
int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);


    scanf("%d%d",&n,&m);

    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
    }

    dfs(1);

    printf("%d\n",ctc);

    for(int i=1;i<=ctc;i++)
    {
        for(auto it:c[i])
            printf("%d ",it);
        printf("\n");
    }
    return 0;


}