#include <bits/stdc++.h>
using namespace std;
int f[26] = {0};
long long int n;
bool pos(long long int req) {
  int cnt = 0;
  for (int i = 0; i < 26; i++) {
    cnt = cnt + (f[i] + req - 1) / req;
  }
  return (cnt <= n);
}
vector<long long int> g[200011];
int main() {
  int n;
  cin >> n;
  int a[n];
  map<long long int, long long int> m;
  for (int i = 0; i < n; i++) cin >> a[i], m[a[i]]++, g[a[i]].push_back(i + 1);
  int cur = 0;
  int ans[n];
  for (int i = 0; i < n; i++) {
    while (cur >= 0) {
      if (m[cur] > 0) {
        m[cur]--;
        ans[i] = cur;
        break;
      }
      cur -= 3;
    }
    if (cur < 0) {
      cout << "Impossible";
      return 0;
    }
    cur++;
  }
  cout << "Possible\n";
  for (int i = 0; i < n; i++) {
    cout << g[ans[i]].back() << " ";
    g[ans[i]].pop_back();
  }
}
