#include <bits/stdc++.h>
using namespace std;
int a[200002];
int sum[200002];
int main() {
  int n, t, k;
  cin >> n >> t >> k;
  for (int i = 1; i <= t; i++) cin >> a[i];
  a[0] = 1;
  int kmin = 0;
  for (int i = 0; i <= t; i++)
    kmin += max(0, a[i] - a[i + 1]), sum[i + 1] = sum[i] + a[i];
  if (k < kmin || k > n - t || sum[t + 1] != n) {
    puts("-1");
    return 0;
  }
  int now = n;
  cout << n << endl;
  for (int i = 1; i <= t; i++) {
    int ind = 0;
    now--;
    for (int j = 0; j < a[i]; j++) {
      cout << sum[i - 1] + ind + 1 << ' ' << sum[i] + j + 1 << endl;
      if ((j < a[i] - 1) && (ind < a[i - 1] - 1) && (k <= now - 1 - t + i))
        ind++, now--;
    }
  }
  return 0;
}
