#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int q[N], n;
stack<int> s[N];
int main() {
  int a;
  while (~scanf("%d", &n)) {
    for (int i = 1; i <= n; ++i) scanf("%d", &a), s[a].push(i);
    int p = 0, i = 0;
    while (1) {
      if (!s[i].empty()) {
        q[p++] = s[i].top();
        ++i;
      } else {
        i = i - 3;
        if (i < 0) break;
        if (!s[i].empty())
          s[i].pop();
        else
          break;
        if (!s[i + 1].empty())
          s[i + 1].pop();
        else
          break;
        if (!s[i + 2].empty())
          s[i + 2].pop();
        else
          break;
      }
    }
    if (p == n) {
      puts("Possible");
      for (int i = 0; i < n - 1; ++i) printf("%d ", q[i]);
      printf("%d\n", q[n - 1]);
    } else
      puts("Impossible");
  }
  return 0;
}
