#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <climits>
#include <cmath>
#include <complex>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <vector>
#include <stack>
using namespace std;
#define ll long long
#define mp make_pair
#define fi first
#define pii pair<int,int>
#define se second
//const int INF=1000000000000000000;
const int INF=1e9;
const int N=1000000;
const int M=998244353;
const int ln=20;
template<typename T>
std::ostream& operator<< (std::ostream& os,pair<T,T> p){
return os << p.fi << "," << p.se << " ";
}
void solve(){
int n,k;
cin >> n >> k;
int a[n];
for(int i=0;i<n;i++) cin >> a[i];
set<pii> s;
for(int i=0;i<n;i++) s.insert(mp(-a[i],i));
vector<vector<int>> ans;
while(!s.empty()){
if(s.size()<k){
cout << -1 << "\n";
return;
}
ans.push_back({});
for(int i=0;i<k;i++){
auto it=s.begin();
ans.back().push_back((*it).se);
s.erase(it);
}
for(int i:ans.back()){
a[i]--;
if(a[i]!=0){
s.insert(mp(-a[i],i));
}
}
}
cout << ans.size() << "\n";
for(auto v:ans){
cout << v.size() << " ";
for(int i:v) cout << i+1 << " ";
cout << "\n";
}
}
signed main(){
auto begin = std::chrono::high_resolution_clock::now();
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int t;
//cin >> t;
t=1;
while(t--) solve();
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
}
