#include <bits/stdc++.h>
using namespace std;
template <class T>
ostream& operator<<(ostream& os, vector<T> V) {
  os << "[ ";
  for (auto v : V) os << v << " ";
  os << "]";
  return os;
}
template <class T>
ostream& operator<<(ostream& os, set<T> second) {
  os << "{ ";
  for (auto s : second) os << s << " ";
  return os << "}";
}
template <class T>
ostream& operator<<(ostream& os, multiset<T> second) {
  os << "{ ";
  for (auto s : second) os << s << " ";
  return os << "}";
}
template <class L, class R>
ostream& operator<<(ostream& os, pair<L, R> P) {
  return os << "(" << P.first << "," << P.second << ")";
}
template <class L, class R>
ostream& operator<<(ostream& os, map<L, R> M) {
  os << "{ ";
  for (auto m : M) os << "(" << m.first << ":" << m.second << ") ";
  return os << "}";
}
template <class L, class R>
ostream& operator<<(ostream& os, unordered_map<L, R> M) {
  os << "{ ";
  for (auto m : M) os << "(" << m.first << ":" << m.second << ") ";
  return os << "}";
}
const long long N = 200010, M = 1e9 + 7;
long long n, a[N];
vector<long long> f[N], sol;
void solve() {
  cin >> n;
  for (long long i = 0; i < n; i++) cin >> a[i];
  for (long long i = 0; i < n; i++) f[a[i]].push_back(i + 1);
  sol = vector<long long>(0);
  long long minus = 0;
  for (long long i = 0; i < n; i++) {
    long long h = i - minus;
    while (h >= 0 && f[h].size() == 0) h -= 3, minus += 3;
    if (h < 0) {
      cout << "Impossible\n";
      return;
    }
    sol.push_back(f[h].back());
    f[h].pop_back();
  }
  cout << "Possible\n";
  for (long long it : sol) cout << it << ' ';
  cout << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(0);
  solve();
  return 0;
}
