#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#define fi first
#define se second
#define ll long long
using namespace std;
const int N = 1e5 + 7;
const int M = 23;
const int mod = 998244353;
int n,k;
int a[N];
set < pair < int , int > > s;
void solve1()
{
cin >> n >> k;
for( int i = 1; i <= n; i++ ){
cin >> a[i];
s.insert({a[i] , i});
}
int ans = 0;
while( !s.empty() ){
if( (int)s.size() < k ){
cout << -1;
return;
}
int sz = 1;
vector < pair < int , int > > v;
while( sz <= k ){
auto x = *--s.end();
s.erase(--s.end());
x.fi--;
v.push_back(x);
sz++;
}
ans++;
for( auto x : v ){
if( x.fi > 0 )s.insert(x);
}
}
for( int i = 1; i <= n; i++ ){
s.insert({a[i] , i});
}
cout << ans << "\n";
while( !s.empty() ){
int sz = 1;
vector < pair < int , int > > v;
cout << 1 << " ";
while( sz <= k ){
auto x = *--s.end();
s.erase(--s.end());
x.fi--;
cout << x.se << " ";
v.push_back(x);
sz++;
}
cout << "\n";
for( auto x : v ){
if( x.fi > 0 )s.insert(x);
}
}
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
//freopen( "input.txt" , "r" , stdin );
//freopen( "output.txt" , "w" , stdout );
int cghf = 1;//cin >> cghf;
while( cghf-- ){
solve1();
}
}
