#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int a[N], b[N], fa[N];
int n, t, k;
int main() {
  while (scanf("%d%d%d", &n, &t, &k) == 3) {
    a[0] = b[0] = 1;
    for (int i = 1; i <= t; i++) {
      scanf("%d", a + i);
      b[i] = a[i - 1] + b[i - 1];
    }
    int mn = a[t], mx = 1;
    for (int i = 1; i <= t; i++) {
      mx += a[i] - 1;
      mn += max(a[i - 1] - a[i], 0);
    }
    if (k >= mn && k <= mx) {
      for (int i = 1; i <= t; i++) {
        for (int j = 0; j < a[i]; j++) {
          fa[j + b[i]] = b[i - 1];
        }
        for (int j = 1; j < min(a[i], a[i - 1]); j++) {
          if (mn < k) {
            mn++;
          } else {
            fa[j + b[i]] = j + b[i - 1];
          }
        }
      }
      printf("%d\n", n);
      for (int i = 2; i <= n; i++) {
        printf("%d %d\n", fa[i], i);
      }
    } else {
      puts("-1");
    }
  }
  return 0;
}
