#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 85 - 69;
int a[maxn], b[maxn], c[maxn], ss[maxn], t, k, n;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> t >> k;
  for (int i = 0; i < t; i++) cin >> a[i];
  int sum = 0;
  for (int i = t - 2; i >= 0; i--) {
    c[i] = max(0, a[i] - a[i + 1]);
    sum += c[i];
    b[i] = min(a[i], a[i + 1]);
  }
  b[t - 1] = a[t - 1];
  ss[0] = 2;
  for (int i = 0; i < t; i++) ss[i + 1] = ss[i] + a[i];
  sum += b[t - 1];
  if (sum > k) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 0; i < t - 1; i++) {
    for (int j = b[i] - 1; j > 0 and sum < k; j--) {
      b[i]--;
      c[i]++;
      sum++;
    }
  }
  if (sum < k) {
    cout << -1 << endl;
    return 0;
  }
  cout << n << '\n';
  for (int j = 0; j < b[0] + c[0]; j++) cout << 1 << ' ' << ss[0] + j << '\n';
  for (int i = 0; i + 1 < t; i++) {
    for (int j = 0; j < b[i]; j++)
      cout << ss[i] + j << ' ' << ss[i + 1] + j << '\n';
    for (int j = b[i]; j < a[i + 1]; j++)
      cout << ss[i] << ' ' << ss[i + 1] + j << '\n';
  }
  return 0;
}
