#include <bits/stdc++.h>
using namespace std;
const int maxn = 222222;
vector<int> v[maxn], answer;
int n;
int a;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a;
    v[a].push_back(i);
  }
  int it = n;
  int cur = 0;
  while (it--) {
    while (cur >= 0 && v[cur].empty()) {
      cur -= 3;
    }
    if (cur < 0) {
      cout << "Impossible\n";
      return 0;
    }
    answer.push_back(v[cur].back());
    v[cur].pop_back();
    cur++;
  }
  cout << "Possible\n";
  for (int i = 0; i < answer.size(); i++)
    cout << answer[i] << " \n"[i + 1 == answer.size()];
  return 0;
}
