#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 7;
int n;
vector<int> id[N];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    id[x].push_back(i + 1);
  }
  int cur = 0;
  vector<int> ans;
  while (n && cur >= 0) {
    while (cur >= 0 && !id[cur].size()) cur -= 3;
    if (cur < 0) return cout << "Impossible\n", 0;
    ans.push_back(id[cur].back());
    id[cur].pop_back();
    n--, cur++;
  }
  cout << "Possible\n";
  for (auto i : ans) cout << i << ' ';
}
