#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll M = 1000000007;
const ll M1 = 998244353;
using vl = vector<ll>;
using pll = pair<ll, ll>;
void solve() {
  int n, x;
  cin >> n;
  vector<pll> b(n);
  vector<pll> a(n);
  for (int i = 0; i < n; i++) {
    cin >> x;
    a[i].first = x;
    a[i].second = i;
  }
  if (a[0].first == 0) {
    cout << -1;
    return;
  }
  int ans = 0, s = 0;
  for (int i = 0; i < n; i++) {
    s += a[i].first;
  }
  if (s < (n - 1)) {
    cout << -1;
    return;
  }
  sort(a.begin() + 1, a.end());
  int pr[101] = {0};
  pr[0] = 1;
  b[0].first = 1;
  b[0].second = a[n - 1].second + 1;
  pr[a[n - 1].second] = 1;
  ans++;
  a[0].first--;
  int i = 1, k = 1, f = 1;
  while (a[0].first && i < n) {
    if (pr[a[i].second] == 0) {
      ans++;
      a[0].first--;
      b[k].first = 1;
      b[k].second = a[i].second + 1;
      pr[a[i].second] = 1;
      k++;
      if (i < n)
        i++;
      else {
        f = 0;
        break;
      }
    } else {
      if (i < n)
        i++;
      else {
        f = 0;
        break;
      }
    }
  }
  if (f) {
    int j = n - 1;
    while (j > i) {
      if (a[j].first) {
        if (pr[a[j - 1].second] == 0) {
          ans++;
          b[k].first = a[j].second + 1;
          b[k].second = a[j - 1].second + 1;
          pr[a[j - 1].second] = 1;
          k++;
          a[j].first--;
        } else {
          if (pr[a[i].second] == 0) {
            ans++;
            b[k].first = a[j].second + 1;
            b[k].second = a[i].second + 1;
            pr[a[i].second] = 1;
            i++;
            k++;
            a[j].first--;
          } else
            i++;
        }
      }
      if (a[j].first == 0) j--;
    }
  }
  cout << ans << "\n";
  for (i = 0; i < ans; i++) {
    cout << b[i].first << " " << b[i].second << "\n";
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t = 1;
  for (int i = 1; i <= t; i++) {
    solve();
  }
  return 0;
}
