#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, t, k;
  cin >> n >> t >> k;
  vector<int> A = {1};
  for (int i = 1; i <= t; i++) {
    int a;
    cin >> a;
    A.push_back(a);
  }
  int min_children = A[t];
  int max_children = A[t];
  for (int i = 1; i < t; i++) min_children += max(0, A[i] - A[i + 1]);
  for (int i = 1; i < t; i++) max_children += A[i] - 1;
  if (k < min_children || k > max_children) {
    cout << -1 << endl;
    return 0;
  }
  cout << n << endl;
  vector<int> BFS = {1};
  int cur = 1;
  int deficit = k - min_children;
  for (int i = 1; i <= t; i++) {
    vector<int> new_BFS;
    int interact = int(BFS.size());
    if (deficit > 0 && int(BFS.size()) > 1) {
      if (A[i] >= A[i - 1]) {
        int cut_back = min(deficit, A[i - 1] - 1);
        deficit -= cut_back;
        interact = A[i - 1] - cut_back;
      }
      if (A[i] < A[i - 1]) {
        int cut_back = min(deficit, A[i] - 1);
        deficit -= cut_back;
        interact = A[i] - cut_back;
      }
    }
    for (int j = 0; j < A[i]; j++) {
      cout << BFS[j % interact] << " " << ++cur << endl;
      new_BFS.push_back(cur);
    }
    BFS = new_BFS;
  }
}
