import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
        Arrays.sort(arr);
        int interval = arr[1] - arr[0];
        if (interval == 0) {
            System.out.println("NO");
            return;
        }
        for (int i = 2; i < n; i++) {
            if (arr[i] - arr[i - 1] != interval) {
                System.out.println("NO");
                return;
            }
        }
        System.out.println("YES");
    }
}