#include <bits/stdc++.h>
using namespace std;
int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int n, t, k;
int a[200005], maxx, b[200005];
vector<int> v[200005];
int cnt = 1, tmp = 0;
int main() {
  n = read();
  t = read();
  k = read();
  for (int i = 1; i <= t; ++i) a[i] = read();
  for (int i = t; i >= 1; --i) {
    maxx += abs(min(0, a[i + 1] - a[i]));
    if (i == t)
      b[i] = a[i];
    else
      b[i] = b[i + 1] + a[i] - 1;
  }
  v[0].push_back(1);
  if (k < maxx || k > n - t) {
    printf("-1\n");
    return 0;
  } else {
    printf("%d\n", n);
    for (int i = 1; i <= t; ++i) {
      if (k < n - t - tmp) {
        v[i].push_back(++cnt);
        printf("%d %d\n", v[i - 1][0], v[i][0]);
        a[i]--;
        for (int j = 1; j < v[i - 1].size() && a[i] && k < n - t - tmp; ++j) {
          v[i].push_back(++cnt);
          printf("%d %d\n", v[i - 1][j], v[i][j]);
          tmp++;
          a[i]--;
        }
        if (a[i]) {
          for (int j = 1; j <= a[i]; ++j) {
            v[i].push_back(++cnt);
            printf("%d %d\n", cnt, v[i - 1][0]);
          }
        }
      } else {
        for (int j = 1; j <= a[i]; ++j) {
          v[i].push_back(++cnt);
          printf("%d %d\n", cnt, v[i - 1][0]);
        }
      }
    }
  }
}
