#include <bits/stdc++.h>
using namespace std;
const int maxn = 200005;
vector<int> v[maxn], ans;
int n;
int main() {
  while (cin >> n) {
    for (int i = 1; i <= n; i++) {
      int x;
      scanf("%d", &x);
      v[x].push_back(i);
    }
    int cur = 0;
    bool flag = true;
    while (ans.size() < n) {
      while (cur >= 0 && v[cur].empty()) cur -= 3;
      if (cur < 0) {
        flag = false;
        break;
      }
      ans.push_back(v[cur].back());
      v[cur].pop_back();
      cur++;
    }
    if (flag) {
      cout << "Possible" << endl;
      int sz = ans.size();
      for (int i = 0; i < sz; i++)
        printf("%d%c", ans[i], i == sz - 1 ? '\n' : ' ');
    } else
      cout << "Impossible" << endl;
  }
  return 0;
}
