#include <bits/stdc++.h>
using namespace std;
int n;
bool valid = true;
vector<int> seq;
vector<int> pos[200010];
int main() {
  cin >> n;
  for (int i = 0; i < n; ++i) {
    int x;
    cin >> x;
    pos[x].push_back(i + 1);
  }
  int x = 0;
  for (int i = 0; i < n; i++) {
    while (x >= 0 && pos[x].empty()) {
      x -= 3;
    }
    if (x < 0) {
      cout << "Impossible" << endl;
      return 0;
    }
    seq.push_back(pos[x].back());
    pos[x].pop_back();
    x++;
  }
  cout << "Possible" << endl;
  for (int i = 0; i < n - 1; ++i) {
    cout << seq[i] << " ";
  }
  cout << seq[n - 1] << endl;
  return 0;
}
