//STATUS:C++_AC_840MS_6272KB

 #include <functional>

 #include <algorithm>

 #include <iostream>

 //#include <ext/rope>

 #include <fstream>

 #include <sstream>

 #include <iomanip>

 #include <numeric>

 #include <cstring>

 #include <cassert>

 #include <cstdio>

 #include <string>

 #include <vector>

 #include <bitset>

 #include <queue>

 #include <stack>

 #include <cmath>

 #include <ctime>

 #include <list>

 #include <set>

 #include <map>

 using namespace std;

 //using namespace __gnu_cxx;

 //define

 #define pii pair<int,int>

 #define mem(a,b) memset(a,b,sizeof(a))

 #define lson l,mid,rt<<1

 #define rson mid+1,r,rt<<1|1

 #define PI acos(-1.0)

 //typedef

 //typedef __int64 LL;

 //typedef unsigned __int64 ULL;

 //const

 const int N=;

 const int INF=0x3f3f3f3f;

 const int MOD=,STA=;

 //const LL LNF=1LL<<60;

 const double EPS=1e-;

 const double OO=1e15;

 const int dx[]={-,,,};

 const int dy[]={,,,-};

 const int day[]={,,,,,,,,,,,,};

 //Daily Use ...

 inline int sign(double x){return (x>EPS)-(x<-EPS);}

 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}

 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}

 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}

 template<class T> inline T Min(T a,T b){return a<b?a:b;}

 template<class T> inline T Max(T a,T b){return a>b?a:b;}

 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}

 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}

 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}

 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}

 //End

 struct Node{

     int l,r;

     int idx;

     bool operator < (const Node &a)const {

         return l!=a.l?l<a.l:r<a.r;

     }

 }p[N];

 int cnt[N];

 vector<int> q[N];

 int n;

 int main()

 {

   //  freopen("in.txt","r",stdin);

     int i,j,tot,R;

     while(~scanf("%d",&n))

     {

         tot=;

         mem(cnt,);

         for(i=;i<=n;i++)q[i].clear();

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

             scanf("%d%d",&p[i].l,&p[i].r);

             p[i].idx=i+;

         }

         sort(p,p+n);

         R=-;

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

             if(p[i].l>=R){

                 tot++;

                 R=p[i].r;

             }

             R=Min(R,p[i].r);

             q[tot].push_back(p[i].idx);

             cnt[tot]++;

         }

         printf("%d\n",tot);

         for(i=;i<=tot;i++){

             printf("%d",q[i][]);

             for(j=;j<cnt[i];j++)

                 printf(" %d",q[i][j]);

             putchar('\n');

         }

         putchar('\n');

     }

     return ;

 }