#include <bits/stdc++.h>
#define pb push_back
#define ff first
#define ss second
#define LLA(x) x.rbegin(),x.rend()
#define print(x) for(auto el:x)cout<<el<<' ';cout<<"\n";
#define printPII(x) for(auto [a,b]:x)cout<<a<<","<<b<<' ';cout<<'\n';
using namespace std;
using PII = pair <int, int>;
using ll = long long;
int n, k;
bool impossible;
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
cin >> n >> k;
vector <vector <int> > ans;
set <PII> bfs;
ll sum = 0;
for (int i = 1; i <= n; i++) {
int x; cin >> x;
sum += x;
bfs.insert({x, i});
}
while(!impossible && sum > 0) {
vector <int> pick(1, 1);
vector <PII> add;
for (int i = 0; i < k; i++) {
auto it = --bfs.end();
PII cur = *it;
bfs.erase(it);
pick.pb(cur.ss);
cur.ff--;
sum--;
if (cur.ff < 0) {
impossible = 1;
break;
}
add.pb(cur);
}
ans.pb(pick);
for (auto el : add) bfs.insert(el);
}
// int dbg = 0;
if (impossible) {
cout << "-1\n";
return 0;
}
cout << ans.size() << '\n';
for (auto el : ans) {
print(el);
}
}
