#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int n, ans[N];
set<pair<int, int> > a[3];
signed main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    a[x % 3].insert({x, i});
  }
  int curr = 0;
  for (int i = 0; i < n; i++) {
    set<pair<int, int> >::iterator it = a[curr % 3].lower_bound({curr, -1});
    pair<int, int> c;
    if (it != a[curr % 3].end() && (*it).first == curr) {
      c = *it;
      ans[i] = c.second + 1;
    } else {
      if (it == a[curr % 3].begin()) {
        cout << "Impossible";
        return 0;
      } else {
        it--;
        c = *it;
        ans[i] = c.second + 1;
      }
    }
    a[curr % 3].erase(c);
    curr = c.first + 1;
  }
  cout << "Possible\n";
  for (int i = 0; i < n; i++) cout << ans[i] << ' ';
  return 0;
}
