#include<bits/stdc++.h>
#define maxn 1000005
using namespace std;
int n,Ans,Min,Max[maxn],f[maxn],lst[maxn],L,R,mid;
struct lc{
int x,id;
bool operator <(const lc b)const{return x<b.x;}
}a[maxn];
inline int read(){
int ret=0;char ch=getchar();
while (ch<'0'||ch>'9') ch=getchar();
while (ch<='9'&&ch>='0') ret=ret*10+ch-'0',ch=getchar();
return ret;
}
inline int check(int len){
memset(lst,0,sizeof lst);
memset(f,-1,sizeof f);
memset(Max,-1,sizeof Max);
Max[0]=0;int inf=Max[1];
for (int i=1;i<=n;i++){
if (a[i].x<=i&&Max[i-a[i].x]>=0&&lst[i-a[i].x]+len>=i) f[i]=Max[i-a[i].x]+1; //判断是否能新成一个组
if (f[i]>=Max[i-1]) lst[i]=i,Max[i]=f[i];
else lst[i]=lst[i-1],Max[i]=Max[i-1];
}
return f[n]; //返回最大组数
}
int main(){
n=read();
for (int i=1;i<=n;i++) a[i]=(lc){read(),i};
sort(a+1,a+n+1);
printf("%d\n",Min=check(n)); //记录最大组数
L=0,Ans=R=n;
while (L<=R){
mid=L+R>>1;
if (check(mid)==Min) Ans=mid,R=mid-1; //查找满足最大组数的前提下mid最小为多少
else L=mid+1;
}
check(Ans),R=n; //最后要在check一遍来计算lst数组
while (R){
L=lst[R-a[R].x];
printf("%d",R-L);
for (int i=L+1;i<=R;i++) printf(" %d",a[i].id); //输出答案
putchar('\n');R=L;
}
return 0;
}
