#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<ll,int> pii;
const int maxn = 1e6 + 10;
ll a[maxn];
int i,n,t,k;
vector<pair<ll,vector<int>>>res;
priority_queue<pii> q;
bool solve(ll val)
{
vector<int> ans;
ans.reserve(k);
for(int i = 1;i<=k;i++)
{
if(q.top().fi<val)
{
for(const int& l : ans)q.push(mk(a[l],l));
return 0;
}
else
{
ans.pb(q.top().se);
q.pop();
}
}
for(const int&l : ans)
{
a[l]-=val;
q.push(mk(a[l],l));
}
res.pb(mk(val,ans));
return 1;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>k;
res.reserve(n*k);
for(i = 1;i<=n;i++)
{
cin>>a[i];
q.push(mk(a[i],i));
}
for(ll tmp = LLONG_MAX;tmp;tmp>>=1)
{
while(solve(tmp));
}
if(q.top().fi)
{
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;
}
