#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define sz(c) (int)(c).size()
#define all(c) (c).begin(), (c).end()
#define in freopen("input.txt", "r", stdin);
#define out freopen("output.txt", "w", stdout);
using namespace std;
const int N = 2 * 1e5 + 10;
const int MOD = 1e9 + 7;
const int INF = 1e9;
int TN = 1;
int n, k;
set<pair<int, int>> st;
vector<vector<int>> ans;
void solve() {
cin >> n >> k;
for (int i = 1; i <= n; i++) {
int x; cin >> x; st.insert({-x, i});
}
while (!st.empty()) {
if (sz(st) == 1) {
cout << -1 << "\n"; return;
}
auto a = *st.begin(); st.erase(st.begin());
auto b = *st.begin(); st.erase(st.begin());
if (a.fi != -1) {
st.insert({a.fi + 1, a.se});
}
if (b.fi != -1) {
st.insert({b.fi + 1, b.se});
}
vector<int> cur; cur.pb(1); cur.pb(a.se); cur.pb(b.se);
ans.pb(cur);
}
cout << sz(ans) << "\n";
for (auto i: ans) {
for (auto j: i) {
cout << j << " ";
}
cout << endl;
}
return;
}
signed main() {
// ios_base::sync_with_stdio(0);
// in; out; // cin >> TN;
while (TN--) solve();
return 0;
}
