def main():
    n = int(input())
    l = [int(i) for i in input().split()]
    if len(l) != len(list(set(l))):
        print("NO")
    else:
        sorted_list = sorted(l)
        diff = sorted_list[1] - sorted_list[0]
        for i in range(len(sorted_list) - 1):
            if diff != sorted_list[i+1] - sorted_list[i]:
                print("NO")
                return
        print("YES")

if __name__ == '__main__':
    main()