#include <bits/stdc++.h>
using namespace std;
long long a[200009], n, t, k, mx, mn, gh, ver, ca;
int main() {
  a[0] = 1;
  mx = 1;
  cin >> n >> t >> k;
  for (long long i = 1; i < t + 1; i++) {
    cin >> a[i];
    mn += max(a[i - 1] - a[i], (long long)0);
    mx += a[i] - 1;
  }
  mn += a[t];
  if (k < mn || k > mx) {
    cout << -1;
    return 0;
  }
  cout << n << endl;
  ver = 2;
  gh = 1;
  for (long long i = 1; i < t + 1; i++) {
    ca = a[i];
    for (long long j = gh; j < gh + a[i - 1] - 1; j++) {
      if (mx > k && a[i] > 1) {
        mx--;
        cout << j << " " << ver << endl;
        a[i]--;
        ver++;
      }
    }
    for (long long j = 0; j < a[i]; j++) {
      cout << gh + a[i - 1] - 1 << " " << ver << endl;
      ver++;
    }
    a[i] = ca;
    gh = gh + a[i - 1];
  }
}
