/*
TASK: siuu
*/
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 400005
#define ff first
#define ss second
#define pb push_back
#define sz(s) (int)s.size()
#define rep(c, a, b) for(c = a; c <= b; c++)
ll n, t, m, l, jog;
deque <int> v, ans;
pair <int,int> a[N];
vector <deque<int>> answer;
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n >> m;
for(int i = 1;i <= n; i++) {
cin >> a[i].ff;
if(a[1].ff != a[i].ff) t = 1;
a[i].ss = i;
}
if(t) {
if(n % m) return cout << "-1\n", 0;
}
l = 1;
sort(a + 1, a + n + 1);
for(int i = 1; i <= n; i++) {
v.pb(a[i].ss);
if(sz(v) == m) {
ans.pb(a[l].ff);
answer.pb(v);
for(int j = l + 1; j <= i; j++) {
a[j].ff -= a[l].ff;
}
a[l].ff = 0;
while(l <= n && a[l].ff == 0) {
v.pop_front();
l++;
}
}
}
if(l != n + 1) {
cout << "-1\n";
return 0;
}
t = sz(answer);
if(t * m > 3e6) {
cout << "-1\n";
return 0;
}
cout << sz(answer) << '\n';
for(auto i : answer) {
cout << ans[0] << " ";
for(auto j : i) {
cout << j << " ";
}
ans.pop_front();
cout << '\n';
}
}
