#include <bits/stdc++.h>
using namespace std;
template <class T, class U>
ostream& operator<<(ostream& o, const pair<T, U>& v) {
  return o << "(" << v.first << ", " << v.second << ")";
}
template <class T>
ostream& operator<<(ostream& o, const vector<T>& v) {
  o << "{";
  for (int i = 0; i < (int)((int)((v).size())); ++i)
    o << (i ? ", " : "") << v[i];
  return o << "}";
}
template <class T, class U>
ostream& operator<<(ostream& o, const map<T, U>& v) {
  o << "{";
  for (const auto& e : v) o << e << ", ";
  return o << "}";
}
template <class T>
string to_s(const T& v) {
  ostringstream is;
  is << v;
  return is.str();
}
const int dx[] = {0, -1, 0, 1};
const int dy[] = {-1, 0, 1, 0};
int main(int argc, char* argv[]) {
  int n;
  cin >> n;
  vector<queue<int> > in(n + 1);
  for (int i = 0; i < (int)(n); ++i) {
    int t;
    cin >> t;
    in[t].push(i);
  }
  vector<int> ans;
  int num = 0;
  while (true) {
    while (num >= 3 && in[num].empty()) {
      num -= 3;
    }
    if (in[num].empty()) break;
    ans.push_back(in[num].front());
    in[num].pop();
    ++num;
  }
  if ((int)((ans).size()) < n)
    cout << "Impossible" << '\n';
  else {
    cout << "Possible" << '\n';
    for (int i = 0; i < (int)((int)((ans).size())); ++i) {
      if (i) cout << ' ';
      cout << ans[i] + 1;
    }
    cout << '\n';
  }
}
