#include <iostream>

#include <string.h>

using namespace std;

const int MAX_N=;

const int MAX_M=;

struct edge{

    int v,next;

    int len;

}E[MAX_M];

int p[MAX_N],eid;

void init(){

    memset(p,-,sizeof(p));

    eid=;

}

void insert(int u,int v){

    E[eid].v=v;

    E[eid].next=p[u];

    p[u]=eid++;

}

void tarjan(int u){

    dfn[u]=low[u]=++idx;

    s[top++]=u;

    in_stack[u]=true;

    for(int i=p[u];i+;i=E[i].next){

        int v=E[i].v;

        if(!dfn[v]){

            tarjan(v);

            low[u]=min(low[u],low[v]);

        }else if(in_stack[v]){

            low[u]=min(low[u],dfn[v]);

        }

    }

    if(dfn[u]==low[u]){

        ++scc;

        do{

            belong[s[--top]]=scc;

            in_stack[s[top]]=false;

        }while(s[top]!=u);

    }

}

int main() {

    int n,m;

    init();

    cin>>n>>m;

    for(int i=;i<m;i++){

        int u,v;

        cin>>u>>v;

        insert(u,v);

    }

    memset(dfn,,sizeof(dfn));

    idx=;

    for(int i=;i<=n;++i){

        if(!dfn[i]){

            tarjan(i);

        }

    }

    for(int i=;i<=scc;i++){

        cout<<"block "<<i<<": ";

        for(int j=;j<=n;j++){

           if(belong[j]==i){

              cout<<j<<" ";

           }

        }

        cout<<endl;

    }

    return ;

}