def eql_space(xs:list):
    space = abs(xs[0] - xs[1])
    check = lambda x,y:abs(x - y) == space
    xlen = len(xs)
    if len(list(set(xs))) != xlen:
        return False
    for i in range(1,xlen - 1):
        if not check(xs[i],xs[i + 1]):
            return False
    return True

N = int(input())
xs = [int(x) for x in input().split()]
xs.sort()
print("YES" if eql_space(xs) else "NO")