import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public class No406 {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int count = s.nextInt();
        Integer[] arr = new Integer[count];
        String out = "YES";
        for (int i = 0; i < count; i++) {
            arr[i] = s.nextInt();
        }
        Arrays.sort(arr, Comparator.reverseOrder());
        int diff = arr[1] - arr[0];
        if (diff == 0) {
            out = "NO";
        } else {
            for (int i = 1; i < count; i++) {
                if (arr[i] - arr[i - 1] != diff) {
                    out = "NO";
                    break;
                }
            }
        }
        System.out.println(out);
    }
}