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

const int maxn=5e5+10;

inline int read(){
    int x=0,w=1;char c=getchar();
    while(c<'0'||c>'9'){if(c=='-')w=-1;getchar();}
    while(c<='9'&&c>='0'){x=(x<<3)+(x<<1)+c-'0';c=getchar();}
    return x*w;
}

int n,m;
struct Graph{
    vector<int> E[maxn];
    inline void add_edge(int u,int v){
        E[u].push_back(v);
    }
    int dfn[maxn],dfncnt,low[maxn];
    int scc[maxn],scccnt;
    vector<int> SCC[maxn];
    int st[maxn],top;
    void Tarjan(int u){
        dfn[u]=++dfncnt,low[u]=dfn[u];
        st[++top]=u;
        for(int v:E[u]){
            if(!dfn[v]){
                Tarjan(v);
                low[u]=min(low[u],low[v]);
            }
            else if(!scc[v]) low[u]=min(low[u],dfn[v]);
        }
        if(dfn[u]==low[u]){
            ++scccnt;
            while(st[top]!=u){
                scc[st[top]]=scccnt;
                SCC[scccnt].push_back(st[top]);
                --top;
            }
            scc[u]=scccnt;
            SCC[scccnt].push_back(u);
            --top;
        }
    }
    inline void solve(){
        for(int u=1;u<=n;++u){
            if(!dfn[u]) Tarjan(u);
        }
        printf("%d\n",scccnt);
        for(int i=1;i<=scccnt;++i){
            printf("%ld ",SCC[i].size());
            for(int u:SCC[i]) printf("%d ",u-1);
            printf("\n");
        }
    }
}G;

int main(){
    n=read(),m=read();
    for(int i=1;i<=m;++i){
        int u=read()+1,v=read()+1;
        G.add_edge(u,v);
    }
    G.solve();
    return 0;
}