#include <bits/stdc++.h>
using namespace std;
#define fast ios::sync_with_stdio(0);cin.tie(0);
typedef long long ll;
#define f first
#define s second
#define LOGN 20
const ll MOD = 998244353;
const ll MAXN = 1e5 + 100;
int N, D;
vector<vector<int>> ans;
vector<int> days[MAXN];
deque<pair<int,int>> dq;
bool check(int mid) {
dq = deque<pair<int,int>>();
ans.clear();
for (int i = 1; i <= N; i++) {
ans.emplace_back(vector<int>());
for (auto u : days[i]) {
dq.push_back({i + D, u});
}
int Q = mid;
while (Q && dq.size()) {
pair<int,int> P = dq.front();
if (P.f < i)
return false;
ans.back().push_back(P.s);
dq.pop_front();
Q--;
}
}
return dq.empty();
}
int main() {
fast
int M, Q;
cin >> N >> D >> M;
for (int i = 0; i < M; i++) {
cin >> Q;
days[Q].push_back(i+1);
}
int L = 1;
int R = M;
int res = -1;
vector<vector<int>> ANS;
while (R >= L) {
int mid = L + (R - L) / 2;
if (check(mid)) {
ANS = ans;
res = mid;
R = mid - 1;
} else
L = mid + 1;
}
cout << res << endl;
for (auto u : ANS) {
for (auto v : u)
cout << v << " ";
cout << "0" << endl;
}
}
