#include <bits/stdc++.h>
//#include <ext/pb_ds/detail/standard_policies.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//#pragma GCC optimize("Ofast")
//#pragma GCC target("avx2")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
using namespace std;
//using namespace __gnu_pbds;
//template <typename T> using ordered_set = tree <T, null_type, less < T >, rb_tree_tag, tree_order_statistics_node_update>;
mt19937 gen(time(0));
#define ll long long
#define ld long double
#define pb push_back
#define F first
#define S second
#define TIME clock() * 1.0 / CLOCKS_PER_SEC
#define sz(a) int32_t(a.size())
#define endl '\n'
//#define int long long
const int N = 4e6 + 100;
const int M = 18;
const int mod = 998244353;
const int inf = 1e9 + 7;
pair < ll, int > a[N];
set < pair < pair < int, int >, pair < ll, int > > > st;
vector < int > ans[N];
int nxt[1000100];
int get(int i)
{
if (i == -1 || a[i].F) return i;
return nxt[i] = get(nxt[i]);
}
int32_t main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#else
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
#endif // LOCAL
int n, k;
cin >> n >> k;
ll sum = 0, mx = 0;
for(int i = 0; i < n; i++)
{
cin >> a[i].F;
mx = max(mx, a[i].F);
sum += a[i].F;
a[i].S = i;
nxt[i] = i + 1;
}
nxt[n - 1] = -1;
if (sum % k || mx > sum / k)
{
cout << -1;
return 0;
}
sort(a, a + n);
reverse(a, a + n);
int uk = 1;
st.insert({{0, 0}, {sum / k, 0}});
vector < pair < ll, int > > ve;
while (sz(st))
{
pair < pair < int, int >, pair < ll, int > > p = *st.begin();
st.erase(st.begin());
int sz = p.F.F, i = get(p.F.S), numb = p.S.S; ll k = p.S.F;
if (i == -1)
{
ve.pb({k, numb});
continue;
}
if (a[i].F >= k)
{
a[i].F -= k;
ans[numb].pb(a[i].S);
st.insert({{sz + 1, i + 1}, {k, numb}});
continue;
}
for(auto to: ans[numb])
ans[uk].pb(to);
ans[uk].pb(a[i].S);
st.insert({{sz, i + 1}, {k - a[i].F, numb}});
st.insert({{sz + 1, i + 1}, {a[i].F, uk}});
a[i].F = 0;
uk++;
}
cout << uk << endl;
for(auto to: ve)
{
cout << to.F << " ";
for(auto x: ans[to.S])
cout << x + 1 << " ";
cout << endl;
}
}
