#include <bits/stdc++.h>
using namespace std;
bool comp(int a, int b) { return (a > b); }
int jumlah[200005] = {}, indeks[200005] = {};
vector<int> data[200005];
int main() {
  int now = 0, n, x;
  vector<int> ans;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &x);
    jumlah[x]++;
    data[x].push_back(i);
  }
  while (now >= 0) {
    if (jumlah[now] > 0) {
      ans.push_back(data[now][indeks[now]]);
      indeks[now]++;
      jumlah[now]--;
      now++;
    } else
      now -= 3;
  }
  if (ans.size() != n)
    printf("Impossible");
  else {
    printf("Possible\n");
    for (int i = 0; i <= n - 1; i++) printf("%d ", ans[i]);
  }
  return 0;
}
