#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 500003
#define ff first
#define ss second
#define pb push_back
#define sz(s) (int)s.size()
ll n, t, m, jog, mx, sum, cnt = 1, a[N * 10];
vector <vector<ll>> ans;
queue <pair<ll,int>> 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];
sum += a[i];
mx = max(mx,a[i]);
}
if(sum % m != 0 || mx > sum / m) {
cout << "-1\n";
return 0;
}
int inx = 1;
for(int i = 1; i <= n; i++) {
if(jog == sum/m) {
jog = 0;
inx++;
}
if(jog + a[i] <= sum/m) {
jog += a[i];
v[inx].push({a[i],i});
continue;
}
v[inx].push({sum/m - jog,i});
a[i] -= (sum/m - jog);
jog = a[i];
inx++;
v[inx].push({jog,i});
}
while(!v[1].empty()) {
ll mn = LLONG_MAX;
vector <ll> jogap;
for(int i = 1; i <= inx; i++) {
mn = min(mn,v[i].front().ff);
}
jogap.pb(mn);
for(int i = 1; i <= inx; i++) {
jogap.pb(v[i].front().ss);
v[i].front().ff -= mn;
if(!v[i].front().ff) v[i].pop();
}
ans.pb(jogap);
}
cout << sz(ans) << '\n';
for(int i = 0; i < sz(ans); i++) {
for(auto j : ans[i]) {
cout << j << " ";
}
cout << '\n';
}
}
