#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
typedef long long ll;
using namespace std;
using namespace __gnu_pbds;
#define FOR(i, x, y) for(ll i=(x); i<(y); i++)
#define FORNEG(i, x, y) for(ll i=x; i>y; i--)
#define ordered_set tree<ll, null_type,less_equal<ll>, rb_tree_tag,tree_order_statistics_node_update>
#define fast() ios_base::sync_with_stdio(false);cin.tie(NULL)
#define ll int
ll temp;
ll n,d,m;
ll lis[1000001];
vector<pair<ll,ll>> sus;
bool check(ll x){
ll cur = 0;
FOR(i,0,m){
cur += lis[i];
cur -= min(cur,x);
if (cur > x*d){
return false;
}
}
return true;
}
void ans(ll x){
vector<ll> realsus;
queue<pair<ll,ll>> q;
ll cur = 0;
FOR(i,0,n){
while (cur<m && sus[cur].first == i+1){
q.push(sus[cur]);
cur++;
}
ll sus = q.size();
sus = min(sus,x);
FOR(j,0,sus){
cout << q.front().second << " ";
q.pop();
}
cout << 0 << "\n";
}
}
int main(){
cin >> n >> d >> m;
FOR(i,0,m){
cin >> temp;
lis[temp-1] += 1;
sus.push_back(make_pair(temp,i+1));
}
sort(sus.begin(),sus.end());
ll lo = 0;
ll hi = 1000001;
while (lo<hi){
ll mid = (lo+hi)/2;
if (check(mid)){
hi = mid;
}else{
lo = mid+1;
}
}
cout << lo << "\n";
ans(lo);
}
