#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
// #include "temp.cpp"
#include <cstdio>
using namespace std;
#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; print(x); cerr << endl;
#else
#define dbg(x)
#endif
#define sz(x) (int((x).size()))
#define len(x) (int)x.length()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(x) x.clear()
#define uniq(x) x.resize(unique(all(x)) - x.begin());
#define blt __builtin_popcount
#define pb push_back
#define pf push_front
#define popf pop_front
#define popb pop_back
void print(long long t) {cerr << t;}
void print(int t) {cerr << t;}
void print(string t) {cerr << t;}
void print(char t) {cerr << t;}
void print(double t) {cerr << t;}
void print(long double t) {cerr << t;}
void print(unsigned long long t) {cerr << t;}
template <class T> void print(set <T> v);
template <class T> void print(vector <T> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T, class V> void print(pair <T, V> p);
template <class T, class V> void print(T v[],V n) {cerr << "["; for(int i = 0; i < n; i++) {print(v[i]); cerr << " "; } cerr << "]";}
template <class T, class V> void print(pair <T, V> p) {cerr << "{"; print(p.first); cerr << ","; print(p.second); cerr << "}";}
template <class T> void print(vector <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(deque<T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(set <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(multiset <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void print(map <T, V> v) {cerr << "[ "; for (auto i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void print(unordered_map<T, V> v) {cerr << "[ "; for (auto i : v) {print(i); cerr << " ";} cerr << "]";}
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define nl '\n'
// for grid problems
int dx[8] = {-1,0,1,0,1,-1,1,-1};
int dy[8] = {0,1,0,-1,1,1,-1,-1};
// lowest / (1 << 17) >= 1e5 / (1 << 18) >= 2e5 / (1 << 21) >= 1e6
void fastIO() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
}
// file in/out
void setIO(string str = "") {
fastIO();
if (str != "" && str != "input") {
freopen((str + ".in").c_str(), "r", stdin);
freopen((str + ".out").c_str(), "w", stdout);
}
if(str == "input") {
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
}
}
// Indexed Set
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 1e5 + 10;
int n, d, m;
vector<int> adj[N];
void solve_() {
cin >> n >> d >> m;
vector<int> a(m), b(n);
for(int i = 0; i < m; i++) {
cin >> a[i], b[a[i]]++;
adj[a[i]].pb(i + 1);
}
sort(all(a));
auto check = [&](int mid)->bool {
int cnt = 0;
for(int i = 1; i <= n - d; i++) {
cnt += b[i];
cnt = max(0, cnt - mid);
}
return (cnt == 0);
};
int ina = 1, inb = n - 1, answ = -1;
while(ina <= inb) {
int mid = (ina + inb) / 2;
if(check(mid)) {
answ = mid;
inb = mid - 1;
} else {
ina = mid + 1;
}
}
int cnt = 0;
vector<vector<int>> pr;
deque<int> xd;
for(int i = 1; i <= n - d; i++) {
vector<int> curr;
for(int j = 0; j < b[i]; j++) {
xd.pb(adj[i][j]);
}
cnt += b[i];
cnt = max(0, cnt - answ);
int szi = sz(xd);
for(int j = 0; j < min(answ, szi); j++) {
curr.pb(xd.front());
xd.pop_front();
}
curr.pb(0);
pr.pb(curr);
}
for(int i = n - d + 1; i <= n; i++) {
pr.push_back({0});
}
cout << answ << endl;
for(int i = 0; i < sz(pr); i++) {
for(auto j: pr[i]) {
cout << j << " ";
}
cout << endl;
}
}
int main() {
setIO("");
auto solve = [&](int test_case)-> void {
while(test_case--) {
solve_();
}
};
int test_cases = 1;
solve(test_cases);
return 0;
}
