#include <cstdio>
#include <algorithm>
#include <bitset>
#include <vector>
using namespace std;
FILE *f=fopen("ctc.in","r");
FILE *g=fopen("ctc.out","w");
int id[100005],len;
vector <int> G[100005];
vector<vector<int> > compo;
int low[100005];
int st[100005];
bool inst[100005];
bool viz[100005];
int i,N,M,x,y,nr;
int lastid;
void dfs(int nod){
    viz[nod] = 1;
    inst[nod] = 1;
    st[++len] = nod;
    low[nod] = id[nod] = ++lastid;
    for(auto it:G[nod]){
        if(!viz[it]){
            dfs(it);
        }
        if(inst[it]){
            low[nod] = min( low[nod],low[it] );
        }
    }
    if(low[nod] == id[nod]){
        vector<int> tmp;
        while(st[len] != nod){
            tmp.push_back(st[len]);
            inst[st[len]] = 0;
            len--;
        }
        tmp.push_back(st[len]);
        inst[st[len]] = 0;
        len--;
        compo.push_back(tmp);
    }
}

int main()
{
    fscanf(f,"%d %d",&N,&M);
    for(i=1;i<=M;i++)
    {
        fscanf(f,"%d %d",&x,&y);
        G[x].push_back(y);
    }
    for(int i=1;i<=N;i++)if(!id[i])dfs(i);
    fprintf(g,"%d\n",compo.size());
    for(auto i:compo)
    {
        for(auto it:i)
            fprintf(g,"%d ",it);
        fprintf(g,"\n");
    }
    fclose(f);
    fclose(g);
    return 0;
}