#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(char ch) {
  string s;
  s += ch;
  return s;
}
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
void no() {
  cout << "Impossible\n";
  exit(0);
}
void yes() { cout << "Possible\n"; }
void solve() {
  int n;
  cin >> n;
  vector<int> ans;
  vector<set<pair<int, int>>> a(3);
  for (int i = (int)0; i < (int)n; i++) {
    int x;
    cin >> x;
    a[x % 3].insert({x, i + 1});
  }
  int next_max = 0;
  while (((long long)ans.size()) != n) {
    int group = next_max % 3;
    if (!((long long)a[group].size())) {
      no();
    } else {
      auto it = a[group].lower_bound({next_max, -1});
      if (it == a[group].end()) {
        it--;
      }
      auto val = *it;
      if (val.first > next_max) {
        if (it == a[group].begin()) no();
        it--;
      }
      val = *it;
      ans.push_back(val.second);
      next_max = val.first + 1;
      a[group].erase(it);
    }
  }
  yes();
  for (int i = (int)0; i < (int)n; i++) {
    cout << ans[i] << " ";
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  for (int tc = 1; tc <= t; tc++) {
    solve();
  }
}
