#include <bits/stdc++.h>
using namespace std;
void WA() {
  cout << "Impossible\n";
  exit(0);
}
void OK() {
  cout << "Possible\n";
  exit(0);
}
int main() {
  int n;
  scanf("%d", &n);
  vector<int> kol(n, 0);
  int mx = -1;
  for (int i = 0; i < n; ++i) {
    int a;
    scanf("%d", &a);
    mx = max(mx, a);
    kol[a]++;
  }
  if (n == 2) OK();
  if (mx == 1) WA();
  if (mx % 2 == 0 && kol[mx / 2] != 1) WA();
  for (int i = mx / 2 + 1; i <= mx; ++i)
    if (kol[i] < 2) WA();
  int ind = mx / 2;
  if (mx % 2 == 0) --ind;
  for (; ind > 0; --ind)
    if (kol[ind]) WA();
  OK();
  return 0;
}
