#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
#define f first
#define s second
int n, d, m;
vector<pii> subs;
bool validate(int k) {
auto it = subs.begin();
int carry = 0;
while (it != subs.end()) {
auto ub = upper_bound(subs.begin(), subs.end(), pii(it->f, m+1));
carry += distance(it, ub) - k;
carry = max(carry, 0);
it = ub;
}
return carry <= k * (n + d - subs.rbegin()->f);
}
int main() {
cin >> n >> d >> m;
int x;
for (int i=0; i<m; i++) {
cin >> x;
subs.push_back({x, i+1});
}
sort(subs.begin(), subs.end());
int lower = 1;
int upper = ceil(m / (float)n);
while (lower < upper) {
int mid = lower + (upper-lower)/2;
if (validate(mid)) {
upper = mid;
} else {
lower = mid+1;
}
}
cout << upper << '\n';
for (int curr = 1; curr <= n; curr++) {
for (int i=0; i<upper && (!subs.empty() && subs.front().f <= curr); i++) {
cout << subs.front().s << ' ';
subs.erase(subs.begin());
}
cout << "0\n";
}
}
