#include <bits/stdc++.h>
using namespace std;
#define LIFESUCKS ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define ll long long
#define ld long double
#define ar array
#include<cstdio>
#define vt vector
#include<fstream>
ifstream fin("measurement.in");
ofstream fout("measurement.out");
#include<fstream>
#define pb push_back
#define all(c) (c).begin(), (c).end()
//#define length(x) (int)(x).size()
#define fi first
#define se second
#define vt vector
using namespace std;
int n, d, m;
const int mxm = 1e6;
vt<pair<int, int>>p;
bool check(int mid){
int cr;
int make = 0;
for(int i = 1; i <= n; i++){
cr = 0;
while(make < m && p[make].first <= i && cr < mid){
make++;
cr++;
}
}
return(make == m);
}
int main()
{
LIFESUCKS;
cin >> n >> d >> m;
for(int i = 0; i < m; i++){
int x; cin >> x;
p.pb({x, i + 1});
}
sort(p.begin(), p.end());
int l = 1;
int ans = -1;
int r = m;
while(l <= r){
int mid = l + (r - l) / 2;
if(check(mid)){
ans = mid; r = mid - 1;
}else{
l = mid + 1;
}
}
cout << ans << "\n";
int cr;
int make = 0;
for(int i = 1; i <= n; i++){
cr = 0;
while(make < m && p[make].first <= i && cr < ans){
cout << p[make].second << " ";
make++;
cr++;
}
cout << 0 << "\n";
}
//for(int i = cr; i < n; i++)cout << 0 << "\n";
return 0;
}
