#include<cstdio>
#include<vector>
#include<bitset>
#include<stack>
using namespace std;
stack<int>s;
bitset<100100>v,x;
vector<int>L[100100],c[100100];
int n,m,i,j,a,b,niv[100100],low[100100],nr;
FILE *f,*g;
int minim(int a,int b){
    if(a<b)
        return a;
    return b;
}
void dfs(int nod){
    int i;
    a++;
    v[nod]=1;
    x[nod]=1;
    low[nod]=a;
    s.push(nod);
    niv[nod]=a;
    for(i=0;i<L[nod].size();i++){
        if(v[L[nod][i]]==0){
            dfs(L[nod][i]);
            low[nod]=minim(low[nod],low[L[nod][i]]);
        }
        if(x[L[nod][i]]){
            low[nod]=minim(low[nod],low[L[nod][i]]);
        }
    }
    int b;
    if(low[nod]==niv[nod]){
        nr++;
        do{
            b=s.top();
            s.pop();
            c[nr].push_back(b);
            x[b]=0;
        }while(b!=nod);
    }
}
int main(){
    f=fopen("ctc.in","r");
    g=fopen("ctc.out","w");
    fscanf(f,"%d%d",&n,&m);
    for(i=1;i<=m;i++){
        fscanf(f,"%d%d",&a,&b);
        L[a].push_back(b);
    }
    a=0;
    for(i=1;i<=n;i++){
        if(v[i]==0){
            dfs(i);
        }
    }
    fprintf(g,"%d\n",nr);
    for(i=1;i<=nr;i++){
        for(j=0;j<c[i].size();j++){
            fprintf(g,"%d ",c[i][j]);
        }
        fprintf(g,"\n");
    }



    fclose(f);
    fclose(g);
    return 0;
}