#include <bits/stdc++.h>
using namespace std;
#define MAXX 1000005
#define ll long long
pair<int,int>j[MAXX];
int n,m,d;
bool check(ll num) {
if(num*n<m)return 0;
for(ll k=0;k<n;k++) {
for(ll i=k*num;i<min((ll)m,(k+1)*num);i++) {
if(j[i].first+d<k+1) return 0;
}
}
return 1;
}
int main(){
cin>>n>>d>>m;
for(int i=0;i<m;i++){
cin>>j[i].first;
j[i].second=i+1;
}
sort(j,j+m);
int r=m,l=0,mid,res=-1;
while(l<=r) {
mid=(l+r)/2;
if(check(mid)) {
res=mid;
r=mid-1;
}
else l=mid+1;
}
cout<<res<<endl;
for(ll k=1;k<n;k++){
for(ll i=k*res;i<min((ll)m,(k+1)*res);i++){
cout<<j[i].second<<" ";
}
cout<<0<<endl;
}
}
