#include <bits/stdc++.h>
using namespace std;
#define all(v) v.begin(),v.end()
#define pb push_back
#define ll long long
#define ld long double
#define fi first
#define se second
#define mk make_pair
typedef pair<int,int> pii;
const int maxn = 1e6 + 10;
ll a[maxn];
int i,n,t,k;
vector<pair<ll,vector<int>>>res;
bool solve(ll val)
{
vector<int> ans;
ans.reserve(k);
for(int i = 1;i<=n;i++)
{
if(a[i]>=val)
{
ans.pb(i);
if(ans.size()==k)break;
}
}
if(ans.size()==k)
{
for(const int& l : ans)a[l]-=val;
res.pb(mk(val,ans));
return 1;
}
return 0;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>k;
for(i = 1;i<=n;i++)
{
cin>>a[i];
}
for(ll tmp = LLONG_MAX;tmp;tmp>>=1)
{
while(solve(tmp))sort(a+1,a+1+n,greater<>());
}
for(i = 1;i<=n;i++)if(a[i])
{
cout<<-1;
return 0;
}
cout<<res.size()<<'\n';
for(pair<ll,vector<int>> & l : res)
{
cout<<l.fi<<' ';
for(int p : l.se)cout<<p<<' ';
cout<<'\n';
}
return 0;
}
