import java.util.Scanner;
public class Main2 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int [] s =new int [n];
for(int i = 0; i < s.length; i++) {
s[i] = sc.nextInt();
}
int j;
for(int i = 1; i < s.length; i++) {
int tem = s[i];
for( j = i; j > 0 && tem < s[j - 1]; j--)
s[j] = s[j-1];
s[j] = tem;
}
int i = 1;
while(i < s.length-1) {
if(!(s[i] - s[i-1] == s[i+1] -s[i])) {
System.out.println("Impossible");
break;
}
i++;
}
if(i == s.length-1)
System.out.println("Possible");
}
}