#include<iostream>
#include<cstdio>
#include<vector>
#include<bitset>
using namespace std;
constexpr int N=500005;
int n,m;
bitset<N>mp[N],rmp[N];
bitset<N>vis;
int out[N],ind;
void dfs(int x)
{
    bitset<N> now;vis[x]=1;
    for(now=mp[x]^(mp[x]&vis);now.any();now=mp[x]^(mp[x]&vis))
        dfs(now._Find_first());
    out[++ind]=x;
}
vector<int>pos;
vector<vector<int>>block;
int tot;
void dfsrev(int x)
{
    pos.push_back(x);
    bitset<N> now;vis[x]=1;
    for(now=rmp[x]^(rmp[x]&vis);now.any();now=rmp[x]^(rmp[x]&vis))
    {
        dfsrev(now._Find_first());
    }
    return;
}
int kosaraju()
{
    vis.reset();ind=0;
    for(int i=1;i<=n;++i) if(!vis[i]) dfs(i);
    vis.reset();int res=0;
    for(int i=n,x;i;--i) if(!vis[out[i]])
    {
        pos.clear();
        dfsrev(out[i]);
        tot++;
        block.emplace_back(pos);
    }
    return res;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr),cout.tie(nullptr);
    cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int u,v;
        cin>>u>>v;
        u++,v++;
        mp[u][v]=1;
        rmp[v][u]=1;
    }
    cerr<<"ed\n";
    kosaraju();
    cout<<tot<<"\n";
    for(int i=0;i<tot;i++)
    {
        int l=block[i].size();
        cout<<l;
        for(int u:block[i])
            cout<<" "<<u-1;
        cout<<"\n";
    }
    return 0;
}

/tmp/ccyFoSr5.o: in function `dfs(int)':
answer.code:(.text+0x7b): relocation truncated to fit: R_X86_64_PC32 against symbol `mp' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text+0xcf): relocation truncated to fit: R_X86_64_PC32 against symbol `mp' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text+0x1a0): relocation truncated to fit: R_X86_64_PC32 against symbol `mp' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text+0x1da): relocation truncated to fit: R_X86_64_PC32 against symbol `mp' defined in .bss section in /tmp/ccyFoSr5.o
/tmp/ccyFoSr5.o: in function `kosaraju()':
answer.code:(.text+0x60b): relocation truncated to fit: R_X86_64_PC32 against symbol `n' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text+0x65d): relocation truncated to fit: R_X86_64_PC32 against symbol `n' defined in .bss section in /tmp/ccyFoSr5.o
/tmp/ccyFoSr5.o: in function `main':
answer.code:(.text.startup+0x33): relocation truncated to fit: R_X86_64_PC32 against symbol `n' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text.startup+0x58): relocation truncated to fit: R_X86_64_PC32 against symbol `m' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text.startup+0x66): relocation truncated to fit: R_X86_64_PC32 against symbol `m' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text.startup+0x8f): relocation truncated to fit: R_X86_64_PC32 against symbol `mp' defined in .bss section in /tmp/ccyFoSr5.o
answer.code:(.text.startup+0x108): additional relocation overflows omitted from the output
collect2: error: ld returned 1 exit status