#include <bits/stdc++.h>
using namespace std;
vector<int> num[4], ans;
vector<int> lis[300000];
int n, temp[300000], tot[300000], maxVal = 0;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &temp[i]);
    tot[temp[i]]++;
    lis[temp[i]].push_back(i);
    if (temp[i] > maxVal) maxVal = temp[i];
  }
  int pos = 0;
  for (int i = 0; i < n; i++) {
    if (i > maxVal) break;
    if (tot[i] == 0 && i < maxVal) {
      printf("Impossible\n");
      return 0;
    }
    int siz = lis[i].size() - 1;
    ans.push_back(lis[i][siz]);
    lis[i].pop_back();
    pos = i;
  }
  for (int i = 0; i < n; i++) {
    while (!lis[i].empty()) {
      num[i % 3].push_back(lis[i][lis[i].size() - 1]);
      lis[i].pop_back();
    }
  }
  pos = (pos + 1) % 3;
  while (ans.size() < n) {
    if (num[pos].empty()) {
      printf("Impossible\n");
      return 0;
    }
    ans.push_back(num[pos][num[pos].size() - 1]);
    num[pos].pop_back();
    pos = (pos + 1) % 3;
  }
  for (int i = 0; i < n - 1; i++) {
    if (temp[ans[i + 1]] - temp[ans[i]] > 1) {
      printf("Impossible\n");
      return 0;
    }
  }
  printf("Possible\n");
  for (int i = 0; i < n; i++) {
    if (i) printf(" ");
    printf("%d", ans[i]);
  }
  printf("\n");
}
