//Challenge: Accepted
#include <iostream>
#include <algorithm>
#include <vector>
#include <utility>
#include <queue>
#define ll long long
#define maxn 1000005
#define pii pair<int, ll>
#define ff first
#define ss second
#define io ios_base::sync_with_stdio(0);cin.tie(0);
using namespace std;
ll a[maxn];
vector<int> val;
int main() {
io
ll n, k;
cin >> n >> k;
ll m = 0;
for (int i = 0;i < n;i++) {
cin >> a[i];
m += a[i];
for (int j = 0;j < a[i];j++) {
val.push_back(i);
}
}
bool poss = m % k == 0;
for (int i = 0;i < n;i++) {
if (a[i] > m / k) {
poss = false;
break;
}
}
if (!poss) {
cout << -1 << endl;
} else {
cout << m / k << "\n";
for (int i = 0;i < m / k;i++) {
cout << 1 << " ";
for (int j = i;j < m;j += m / k) {
cout << val[j]+1 << " ";
}
cout << "\n";
}
}
}
