import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.next());
        List<Long> kamos = new ArrayList<>();

        for (int i = 0; i < N; i++) {
            kamos.add(Long.parseLong(sc.next()));
        }

        boolean kamoFlag = true;
        for (int i = 0; i < N; i++) {
            List<Long> tmpKamos = new ArrayList<>(kamos);
            tmpKamos.remove(i);
            if (tmpKamos.contains(kamos.get(i))) {
                kamoFlag = false;
                break;
            }
        }

        if (!kamoFlag) {
            System.out.println("NO");
        } else {
            Collections.sort(kamos);

            long distance = kamos.get(1) - kamos.get(0);
            for (int i = 1; i < N - 1; i++) {
                if (kamos.get(i+1) - kamos.get(i) != distance) {
                    kamoFlag = false;
                    break;
                }
            }

            if (!kamoFlag) {
                System.out.println("NO");
            } else {
                System.out.println("YES");
            }
        }
    }
}