#include <bits/stdc++.h>
using namespace std;
int n, t, k;
int a[200001];
int par[200001];
int main() {
  if (fopen("test.in", "r")) {
    freopen("test.in", "r", stdin);
  }
  cin >> n >> t >> k;
  for (int i = 0; i < t; i++) cin >> a[i];
  int s1 = 0, s2 = 0;
  for (int i = 0; i < t - 1; i++) {
    s1 += a[i] - 1;
    if (a[i] > a[i + 1]) s2 += a[i] - a[i + 1];
  }
  s1 += a[t - 1];
  s2 += a[t - 1];
  if (k > s1 || k < s2) {
    cout << -1 << '\n';
    return 0;
  }
  cout << n << '\n';
  int diff = s1 - k;
  for (int i = 2; i <= a[0] + 1; i++) par[i] = 1;
  int cur = a[0] + 2;
  for (int i = 1; i < t; i++) {
    for (int j = 0; j < a[i]; j++) {
      if (j == 0 || diff == 0) {
        par[cur + j] = cur - a[i - 1];
      } else {
        if (j < a[i - 1]) {
          par[cur + j] = cur - a[i - 1] + j;
          diff--;
        } else {
          par[cur + j] = cur - a[i - 1];
        }
      }
    }
    cur += a[i];
  }
  for (int i = 2; i <= n; i++) {
    cout << i << " " << par[i] << '\n';
  }
  return 0;
}
