package chelper;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import io.InputReader;
import io.OutputWriter;

public class B {
  public void solve(int testNumber, InputReader in, OutputWriter out) {
    int n = in.nextInt();
    int pol = in.nextInt();
    if (pol == 0) {
      out.print(-1);
      return;
    }

    List<Chelik> cheliki = new ArrayList<>();
    for (int i = 2; i <= n; i++) {
      cheliki.add(new Chelik(i, in.nextInt()));
    }
    Collections.sort(cheliki);
    cheliki.add(0, new Chelik(1, pol));

    List<String> answer = new ArrayList<>();

    int left = 0;
    for (int right = 1; right < n; right++) {
      if (left == right) {
        out.print(-1);
        return;
      }
      if (cheliki.get(left).dzun > 0) {
        answer.add(cheliki.get(left).index + " " + cheliki.get(right).index);
        cheliki.get(left).dzun--;
      } else {
        left++;
        right--;
      }
    }

    out.println(answer.size());
    for (String s : answer) {
      out.println(s);
    }
  }

  class Chelik implements Comparable<Chelik> {
    int index;
    int dzun;

    public Chelik(int index, int dzun) {
      this.index = index;
      this.dzun = dzun;
    }

    @Override
    public int compareTo(Chelik o) {
      return Integer.compare(o.dzun, dzun);
    }
  }
}