#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()
ll n, t, m, jog[N], sum, cnt = 1;
pair <ll,ll> a[N];
deque <pair<ll,ll>> v[N];
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n >> m;
for(int i = 1;i <= n; i++) {
cin >> a[i].ff;
a[i].ss = i;
sum += a[i].ff;
}
sort(a+1,a+n+1);
if(sum % m != 0 || sum / m < a[n].ff) {
cout << "-1\n";
return 0;
}
for(int i = 1; i <= n; i++) {
if(jog[cnt] == sum / m) cnt++;
if(jog[cnt] + a[i].ff <= sum / m) {
v[cnt].pb({a[i].ff,a[i].ss});
jog[cnt] += a[i].ff;
continue;
}
v[cnt].pb({sum / m - jog[cnt], a[i].ss});
a[i].ff -= (sum / m - jog[cnt]);
jog[cnt] += (sum / m - jog[cnt]);
cnt++;
v[cnt].pb({a[i].ff,a[i].ss});
jog[cnt] += a[i].ff;
}
vector <int> ans;
while(1) {
ll mn = v[1][0].ff;
bool tr = 0;
if(sz(v[1]))ans.pb(mn);
for(int i = 1; i <= m; i++) {
if(!sz(v[i])) {
tr = 1;
break;
}
mn = min(mn,v[i][0].ff);
ans.pb(v[i][0].ss);
}
if(tr) break;
for(int i = 1; i <= m; i++) {
v[i][0].ff -= mn;
if(!v[i][0].ff) v[i].pop_front();
}
}
cout << sz(ans) / (m + 1) << '\n';
for(int i = 0; i < sz(ans); i++) {
cout << ans[i] << " ";
if(i % (m + 1) == m) cout << '\n';
}
}
