#include <bits/stdc++.h>
using namespace std;
int n, t, k, cnt;
int a[200010], fa[200010];
vector<int> v[200010];
int main() {
  cin >> n >> t >> k;
  a[0] = 1;
  for (int i = 1; i <= t; i++) cin >> a[i];
  if (a[t] > k || n - t < k) {
    cout << "-1";
    return 0;
  }
  for (int i = 0; i <= t; i++) {
    for (int j = 1; j <= a[i]; j++) v[i].push_back(++cnt);
  }
  for (int i = 0; i <= t; i++) {
    for (int j = 1; j <= a[i]; j++) v[i].push_back(++cnt);
  }
  for (int i = 0; i < a[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]; j++) {
      if (l && j < a[i - 1]) {
        fa[v[i][j]] = v[i - 1][j];
        l--;
      } else
        fa[v[i][j]] = v[i - 1][0];
    }
  }
  if (l) {
    cout << "-1";
    return 0;
  }
  cout << n << endl;
  for (int i = 2; i <= n; i++) cout << fa[i] << " " << i << "\n";
  return 0;
}
