#include <bits/stdc++.h>
using namespace std;
int a[222222];
set<pair<int, int> > m[3];
vector<pair<int, int> > d[222222];
int n;
vector<int> t[222222];
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    t[a[i]].push_back(i + 1);
  }
  vector<int> ans;
  int now = -1;
  for (int i = 0; i < n; i++) {
    now++;
    while (now >= 0 && t[now].empty()) now -= 3;
    if (now < 0) {
      puts("Impossible");
      return 0;
    }
    ans.push_back(t[now][t[now].size() - 1]);
    t[now].pop_back();
  }
  puts("Possible");
  for (int i = 0; i < n; i++) printf("%d ", ans[i]);
}
