#include <bits/stdc++.h>
using namespace std;
long long n, a, b, c, d;
int main() {
  cin >> n >> a;
  if (a == 1) d++;
  if (n == 2) {
    cout << "Possible\n";
    return 0;
  }
  b = c = a;
  n--;
  while (n--) {
    cin >> a;
    if (a == 1) d++;
    b = max(a, b);
    c = min(a, c);
  }
  if (d >= 2)
    cout << "Impossible\n";
  else if ((b + 1) / 2 > c)
    cout << "Impossible\n";
  else
    cout << "Possible\n";
  return 0;
}
