#include <bits/stdc++.h>
using namespace std;
int n, t, k, cnt, a[200010], b[200010];
int main() {
  scanf("%d%d%d", &n, &t, &k);
  if (n - t < k) {
    printf("-1\n");
    return 0;
  }
  a[0] = cnt = 1;
  for (int i = 1; i <= t; i++) {
    scanf("%d", &a[i]);
    if (a[i] > a[i - 1]) {
      cnt += a[i] - a[i - 1];
      b[i] = a[i - 1];
    } else
      b[i] = a[i];
  }
  if (cnt > k) {
    printf("-1\n");
    return 0;
  }
  for (int i = 1; i <= t && cnt < k; i++)
    if (k - cnt > b[i] - 1) {
      cnt += b[i] - 1;
      b[i] = 1;
    } else {
      b[i] -= k - cnt;
      cnt = k;
    }
  printf("%d\n", n);
  cnt = 1;
  for (int i = 1; i <= t; i++) {
    for (int j = 0; j < b[i]; j++)
      printf("%d %d\n", cnt + j, cnt + j + a[i - 1]);
    for (int j = b[i]; j < a[i]; j++)
      printf("%d %d\n", cnt, cnt + j + a[i - 1]);
    cnt += a[i - 1];
  }
  return 0;
}
