import sys
if __name__ == '__main__':
    n = int(input())
    lst = [int(input()) for i in range(n)]
    lst.sorted()
    before = lst[0]
    sa = lst[1] - before
    for i in range(len(lst)):
        if i != 0:
            if lst[i] - before == sa:
                before = lst[i]
                continue
            else:
                print("NO")
                sys.exit(0)
    print("YES")