#include <bits/stdc++.h>
using namespace std;
vector<int> vec[200010];
int main() {
  int n, x, m;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d", &x);
    vec[x].push_back(i + 1);
  }
  int persons = 0;
  vector<int> ans;
  m = n;
  while (m-- > 0) {
    while (persons >= 0 && vec[persons].empty()) persons -= 3;
    if (persons < 0) {
      printf("Impossible\n");
      return 0;
    }
    ans.push_back(vec[persons].back());
    vec[persons].pop_back();
    persons++;
  }
  printf("Possible\n");
  for (int i = 0; i < n; i++) {
    printf("%d ", ans[i]);
  }
  return 0;
}
