import java.util.Arrays;
import java.util.Scanner;
/**
* Created by LXF on 2017/8/12.
*/
public class Main3 {
public static String dengcha(int n, int[] x) {
Arrays.sort(x);
int d = x[1] - x[0];
for (int i = 1; i+1 < n; i++) {
if (x[i + 1] - x[i] != d) {
return "Impossible";
}
}
return "Possible";
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int[] x = new int[n];
for (int i = 0; i < n; i++) {
x[i] = scanner.nextInt();
}
System.out.println(dengcha(n, x));
}
}