#include <bits/stdc++.h>
using namespace std;
int a[105];
int b[105];
int main() {
  int n;
  scanf("%d", &n);
  int ma = 0;
  int i;
  for (i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    ma = max(ma, a[i]);
    b[a[i]]++;
  }
  if (ma == 1 && n != 2) return printf("Impossible\n") * 0;
  int mi = (1 + ma) / 2;
  for (i = 1; i <= n; i++)
    if (a[i] < mi) return printf("Impossible\n") * 0;
  int co = 0;
  if (ma % 2 == 0) {
    for (i = 1; i <= n; i++)
      if (a[i] == ma / 2) co++;
    if (co != 1) return printf("Impossible\n") * 0;
  } else {
    for (i = 1; i <= n; i++)
      if (a[i] == (1 + ma) / 2) co++;
    if (co < 2) return printf("Impossible\n") * 0;
  }
  for (i = mi + 1; i <= ma; i++)
    if (b[i] < 2)
      if (co != 1) return printf("Impossible\n") * 0;
  printf("Possible");
  return 0;
}
