//gm --- akezhon
#include <bits/stdc++.h>
// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define pb push_back
#define pf push_front
#define F first
#define S second
#define all(v) v.begin(),v.end()
#define pii pair<int,int>
#define tm (tl+tr)/2
#define TL v+v, tl, tm
#define TR v+v+1, tm+1, tr
#define DA l <= tl && tr <= r
#define NE r < tl || tr < l
#define double long double
// #define int long long
using namespace std;
const int N=2e5+7;
const int mod=1e9+7;
const int inf=2e9;
void AlemAmenov(){
int n, k;
cin >> n >> k;
int a[n+1];
set<pii>st;
vector<vector<int>>ans;
vector<int>d;
for(int i=1; i <= n; i++){
cin >> a[i];
st.insert({a[i], i});
}
bool ok=1;
while(st.size()){
vector<pii>v;
pii x;
for(int i=1; i <= k; i++){
if(st.empty()){
ok=0;
break;
}
x=*st.rbegin();
v.pb(x);
st.erase(x);
}
if(!ok)break;
vector<int>temp;
for(auto [f, i] : v){
if(f-x.F)st.insert({f-x.F, i});
temp.pb(i);
}
ans.pb(temp);
d.pb(x.F);
}
if(ans.size()*k > 3000000)cout << -1;
else {
cout << ans.size() << '\n';
for(int i=0; i < ans.size(); i++){
cout << d[i] << ' ';
for(int it : ans[i]){
cout << it << ' ';
}
cout << '\n';
}
}
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int RealName=1;
// cin >> RealNam;
// srand(time(0));
while(RealName--)
AlemAmenov();
return 0;
}
