#pragma GCC optimize("Ofast,no-stack-protector")
#include <bits/stdc++.h>
#define int long long
using namespace std;
#define endl "\n"
using ull=unsigned long long;
using pii=pair<int,int>;
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1};
#define OVL(x,s) for(auto y:x) cout<<y<<s; cout<<"\n";
template <typename T> istream& operator>>(istream& is, vector<T> &a) {
copy_n(istream_iterator<T>(is), a.size(), a.begin()); return is;}
#ifdef IOI
template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
void dbg_out() { cout << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__);
#else
#define dbg(...) 1337;
#endif
#define pb push_back
#define F first
#define S second
#define all(v) v.begin(),v.end()
const int maxn = 1e5+100;
const int mod = 1e9+7;
void solve(){
int n;
cin>>n;
vector<int> v(n);
cin>>v;
vector<int> c;
__int128_t p = 1;
__int128_t INF = (1LL<<60);
for(int i = 0;i<n;i++){
p*=v[i];
if(p>INF){
int l = 0;
int r = n-1;
while(v[l]==1){
l++;
}
while(v[r]==1){
r--;
}
cout<<l+1<<" "<<r+1<<endl;
return;
}
if(v[i]>1){
c.pb(i);
}
}
if(c.size()>100){
int l = 0;
int r = n-1;
while(v[l]==1){
l++;
}
while(v[r]==1){
r--;
}
cout<<l+1<<" "<<r+1<<endl;
return;
}
__int128_t pref[n];
__int128_t suff[n];
for(int i = 0;i<n;i++){
pref[i] = v[i];
if(i) pref[i]+=pref[i-1];
}
for(int i = n-1;i>=0;i--){
suff[i] = v[i];
if(i+1<n){
suff[i]+=suff[i+1];
}
}
int l = 0;
int r = 0;
__int128_t best = 0;
for(int i = 0;i<c.size();i++){
__int128_t prod = 1;
for(int j = i;j<c.size();j++){
prod*=v[c[j]];
__int128_t cost = (c[i]?pref[c[i]-1]:0)+(c[j]+1<n?suff[c[j]+1]:0)+prod;
if(cost>best){
l = c[i];
r = c[j];
best = cost;
}
}
}
cout<<l+1<<" "<<r+1<<endl;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n,k;
cin>>n>>k;
if(n%k!=0){
cout<<-1<<endl;
return 0;
}vector<int> v(n);cin>>v;
cout<<n/k<<endl;
for(int i = 0;i<n;i+=k){
cout<<v[0]<<" ";
for(int j = i;j<i+k;j++){
cout<<j+1<<" ";
}
cout<<endl;
}
}
