#include <bits/stdc++.h>
using namespace std;
vector<int> s[200010];
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    int a;
    cin >> a;
    s[a].push_back(i);
  }
  int a = 0, s1[200010];
  for (int i = 0; i < n; i++) {
    while (s[a].empty()) a = a - 3;
    if (a < 0) {
      cout << "Impossible" << endl;
      return 0;
    }
    s1[i] = s[a].back();
    s[a].pop_back();
    a++;
  }
  cout << "Possible" << endl << s1[0];
  for (int i = 1; i < n; i++) cout << ' ' << s1[i];
  cout << endl;
  return 0;
}
