#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair <int, int>
#define fi first
#define se second
#define mp make_pair
#define isz(a) (int)(a).size()
const int NM = 1e5;
int N, K, a[NM+5];
priority_queue <pii> Q;
vector <pii> v;
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N >> K;
for (int i = 1; i <= N; i++){
cin >> a[i];
Q.push(mp(a[i], i));
}
while (!Q.empty()){
if (isz(Q) < K){
cout << -1;
return 0;
}
for (int i = 1; i <= K; i++){
pii P = Q.top();
v.push_back(P);
Q.pop();
}
for (int i = isz(v)-1; i >= isz(v)-K; i--){
pii P = v[i];
P.fi--;
if (P.fi > 0) Q.push(P);
}
}
cout << isz(v)/K << '\n';
while (!v.empty()){
cout << 1 << ' ';
for (int i = 1; i <= K; i++){
cout << v.back().se << ' ';
v.pop_back();
}
cout << '\n';
}
return 0;
}
