#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1000000007;
long long POW(long long a, long long b, long long MMM = MOD) {
  long long ret = 1;
  for (; b; b >>= 1, a = (a * a) % MMM)
    if (b & 1) ret = (ret * a) % MMM;
  return ret;
}
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long lcm(long long a, long long b) {
  if (a == 0 || b == 0) return a + b;
  return a * (b / gcd(a, b));
}
int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
int ddx[] = {0, 0, 1, 1, 1, -1, -1, -1}, ddy[] = {1, -1, 1, 0, -1, 1, 0, -1};
vector<pair<int, int> > ans;
vector<int> v[200005];
int a[200005];
int main() {
  int n, t, k;
  scanf("%d%d%d", &n, &t, &k);
  for (int(i) = (1); (i) <= (n); (i) += (1)) scanf("%d", a + i);
  int c = 0;
  for (int(i) = (1); (i) <= (n); (i) += (1)) c += max(0, a[i] - a[i - 1]);
  if (k < c || k > n - t) return !printf("-1");
  printf("%d\n", n);
  v[0].push_back(1);
  c = 1, a[0] = 1;
  int cnt = n - k - t;
  for (int(i) = (1); (i) <= (t); (i) += (1)) {
    cnt++;
    for (int(ii) = (1); (ii) <= (a[i]); (ii) += (1)) v[i].push_back(++c);
    int tt = a[i], p = 0;
    while (p < a[i - 1] && p < a[i] && tt > 0 && cnt > 0) {
      ans.push_back(make_pair(v[i - 1][p], v[i][p]));
      p++, tt--, cnt--;
    }
    while (p < a[i] && tt > 0) {
      ans.push_back(make_pair(v[i - 1][0], v[i][p]));
      p++, tt--;
    }
  }
  for (pair<int, int> p : ans) printf("%d %d\n", p.first, p.second);
}
