#include <bits/stdc++.h>
using namespace std;
const int maxn = 4e5 + 1;
const double eps = 1e-9;
const int mod = 1000000007;
vector<int> lvl[maxn];
vector<int> g[maxn];
int main() {
  srand(time(NULL));
  ios_base::sync_with_stdio(0);
  int n, d, k;
  cin >> n >> d >> k;
  int cnt = 1;
  lvl[0].push_back(0);
  for (int i = 0; i < d; i++) {
    int t;
    cin >> t;
    while (t--) {
      lvl[i + 1].push_back(cnt++);
    }
  }
  int mn = 0;
  for (int i = 0; i < d; i++) {
    for (int j = 0; j < min(lvl[i].size(), lvl[i + 1].size()); j++) {
      int u = lvl[i][j];
      int v = lvl[i + 1][j];
      g[u].push_back(v);
    }
    if (lvl[i].size() > lvl[i + 1].size())
      mn += lvl[i].size() - lvl[i + 1].size();
    else {
      for (int j = lvl[i].size(); j < lvl[i + 1].size(); j++) {
        int u = lvl[i][0];
        int v = lvl[i + 1][j];
        g[u].push_back(v);
      }
    }
  }
  mn += lvl[d].size();
  if (mn > k) {
    cout << -1;
    return 0;
  }
  k -= mn;
  for (int i = 0; i < d; i++) {
    for (int j = 1; j < lvl[i].size(); j++) {
      int u = lvl[i][0];
      int v = lvl[i][j];
      if (g[v].empty()) break;
      g[u].push_back(g[v][0]);
      g[v].clear();
      k--;
      if (k == 0) break;
    }
    if (k == 0) break;
  }
  if (k) {
    cout << -1;
    return 0;
  }
  cout << n << endl;
  for (int u = 0; u < n; u++) {
    for (int v : g[u]) {
      cout << u + 1 << " " << v + 1 << endl;
    }
  }
  return 0;
}
