#include <bits/stdc++.h>
#include <bits/extc++.h>
using namespace __gnu_pbds;
using namespace std;
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define ff first
#define sc second
#define pb push_back
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define ull unsigned long long
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rngl(chrono::steady_clock::now().time_since_epoch().count());
// #define int long long
// #define int unsigned long long
// #define ordered_set(T) tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>
// #define ordered_multiset(T) tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>
const ll mod = 1e9 + 7;
// const ll mod = 998244353;
const ll inf = 1e9;
const ll biginf = 1e18;
const int maxN = 1e5 + 15;
const int maxM = 1e6 + 15;
vector<int> pos[maxN];
int n, d, m, arr[maxM];
bool check(int p) {
int j = 1, did = 0, now;
for (int i = 1; i <= n; i++) {
now = p;
while (j <= i && (int)pos[j].size() - did <= now) { now -= (int)pos[j].size() - did; j++; did = 0; }
if (i - j >= d) return 0;
did = now;
}
return 1;
}
void solve() {
cin >> n >> d >> m;
for (int i = 1; i <= m; i++) {
cin >> arr[i]; pos[arr[i]].pb(i);
}
int l = 1, r = m, m, ans = -1;
while (l <= r) {
m = (l + r) / 2;
if (check(m)) {
ans = m; r = m - 1;
} else l = m + 1;
}
cout << ans << '\n';
for (int i = 1; i <= n; i++) {
int cnt = min(ans, (int)pos[i].size());
while (cnt--) {
cout << pos[i].back() << ' '; pos[i].pop_back();
}
cout << "0\n";
}
}
int32_t main() {
// #ifndef ONLINE_JUDGE
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
// #endif
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
cout << '\n';
}
return 0;
}
