#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
int a[N], par[N];
vector<int> v[N];
int main() {
  int n, t, k, sum = 0;
  cin >> n >> t >> k;
  for (int i = 1; i <= t; i++) {
    cin >> a[i];
    sum += a[i] - 1;
    if (i == t) sum++;
  }
  if (sum < k) {
    cout << "-1\n";
    return 0;
  }
  int diff = sum - k;
  int h = t, cnt = 2, p = 1;
  for (int i = 1; i <= t; i++) {
    for (int j = 1; j <= a[i]; j++) {
      if (j < a[i]) v[i].push_back(cnt);
      par[cnt++] = p;
    }
    p = cnt - 1;
  }
  for (int i = h - 1; i >= 0; i--) {
    int cur = min(diff, min(int(v[i].size()), int(v[i + 1].size())));
    for (int j = 0; j < cur; j++) {
      par[v[i + 1][j]] = v[i][j];
    }
    diff -= cur;
  }
  if (diff > 0) {
    cout << "-1\n";
    return 0;
  }
  cout << n << "\n";
  for (int i = 2; i <= n; i++) cout << i << " " << par[i] << "\n";
}
