#include <bits/stdc++.h>
#define int long long
#define ll long long
using namespace std;
int dx[8] = {1, 0, -1, 0, -1, 1, -1, 1};
int dy[8] = {0, 1, 0, -1, -1, 1, 1, -1};
int n,d,m;
vector<pair<int,int>>v;
bool can(int md){
int cnt = 0;
int day = 1;
bool ok = 1;
for(int i=0 ; i<m ; i++){
if(day<v[i].first)day = v[i].first,cnt = 0;
if(day-v[i].first>d){
ok = 0;
break;
}
cnt++;
if(cnt==md)day++,cnt=0;
}
if(!ok)return ok;
if(day<=n || (day==n+1 && cnt==0))return 1;
return 0;
}
void solve() {
cin>>n>>d>>m;
v = vector<pair<int,int>>(m);
for(int i=0 ; i<m ; i++){
cin>>v[i].first;
v[i].second=i+1;
}
std::sort(v.begin(), v.end());
int l =1 , r=1e9;
int best = -1;
while(l<=r){
int md = (l+r)>>1;
if(can(md)){
best = md;
r = md - 1;
}else l = md + 1;
}
int j = 0;
cout<<best<<endl;
for(int i=0 ; i<n ; i++){
for(int w = j ; w<min(j+best,m) ; w++){
cout<<v[w].second<<" ";
}
cout<<0<<endl;
j+=best;
}
}
int32_t main() {
ios_base::sync_with_stdio(false),
cout.tie(nullptr),
cin.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
cout << endl;
}
return 0;
}
