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