|1/2004-1/2003|+|1/2003-1/2002|+|1/2002-1/2001|+|1/2001-1/2004|等于多少?

问题描述:

|1/2004-1/2003|+|1/2003-1/2002|+|1/2002-1/2001|+|1/2001-1/2004|等于多少?