#include <bits/stdc++.h>
using namespace std;
const int dx[9] = {0, 1, -1, 0, 0, -1, -1, 1, 1};
const int dy[9] = {0, 0, 0, -1, 1, -1, 1, -1, 1};
const double pi = acos(-1.0);
const int N = 2e5 + 100;
int n, t, k, a[N], tot, fa[N];
vector<int> v[N];
int main() {
  ios::sync_with_stdio(0), cin.tie(0);
  cin >> n >> t >> k;
  for (int i = 1; i <= t; i++) cin >> a[i];
  a[0] = 1;
  if (a[t] > k) return cout << -1 << endl, 0;
  for (int i = 0; i <= t; i++)
    for (int j = 1; j <= a[i]; j++) v[i].push_back(++tot);
  for (int i = 0; i <= a[1] - 1; i++) fa[v[1][i]] = 1;
  for (int i = 2; i <= t; i++) fa[v[i][0]] = v[i - 1][0];
  int l = n - t - k;
  for (int i = 2; i <= t; i++) {
    for (int j = 1; j <= a[i] - 1; j++)
      if (l > 0 && j <= a[i - 1] - 1)
        fa[v[i][j]] = v[i - 1][j], l--;
      else
        fa[v[i][j]] = v[i - 1][0];
  }
  if (l != 0) return cout << -1 << endl, 0;
  cout << n << endl;
  for (int i = 2; i <= n; i++) cout << i << ' ' << fa[i] << endl;
  return 0;
}
