#include <bits/stdc++.h>
using namespace std;
double eps = 0.0000001;
double pi = acos(-1);
long long fastpower(long long b, long long p) {
  long long ans = 1;
  while (p) {
    if (p % 2) {
      ans = (ans * b);
    }
    b = b * b;
    p /= 2;
  }
  return ans;
}
long long fastpowermod(long long b, long long p, long long m) {
  long long ans = 1;
  while (p) {
    if (p % 2) {
      ans = ((ans % m) * (b % m)) % m;
    }
    b = ((b % m) * (b % m)) % m;
    p /= 2;
  }
  return ans % m;
}
string makeitstring(long long n) {
  string ans;
  bool ch = 0;
  if (n < 0) {
    n *= -1;
    ch = 1;
  }
  if (n == 0) {
    ans = "0";
  };
  while (n) {
    long long mo = n % 10;
    mo += 48;
    char m = mo;
    ans = m + ans;
    n /= 10;
  }
  if (ch) {
    ans = '-' + ans;
  }
  return ans;
}
bool compare(double f, double s) { return (abs(f - s) < eps); }
long long gcd(long long a, long long b) {
  while (b != 0) {
    long long a2 = a;
    a = b;
    b = a2 % b;
  }
  return a;
}
const int N = 2e5 + 1;
const int M = 1e9 + 7;
vector<long long> v[N];
vector<long long> ans;
long long n;
void input() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    long long x;
    cin >> x;
    v[x].push_back(i + 1);
  }
}
void solve() {
  int x = 0;
  for (int i = 0; i < n; i++) {
    while (x >= 0 && v[x].empty()) {
      x -= 3;
    }
    if (x < 0) {
      cout << "Impossible" << endl;
      return;
    }
    ans.push_back(v[x].back());
    v[x].pop_back();
    x++;
  }
  cout << "Possible" << endl;
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i] << " ";
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  input();
  solve();
  return 0;
}
