#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  map<int, vector<int>> frec;
  for (int i = 0; i < n; i++) {
    int val;
    cin >> val;
    frec[val].push_back(i);
  }
  int x = 0;
  vector<int> ans(n);
  for (int i = 0; i < n; i++) {
    while (frec[x].empty() && x >= 3) x -= 3;
    if (frec[x].empty()) {
      cout << "Impossible\n";
      return 0;
    }
    ans[i] = frec[x].back() + 1;
    frec[x].pop_back();
    x++;
  }
  cout << "Possible\n";
  for (int i = 0; i < n; i++) cout << ans[i] << " ";
  return 0;
}
