To express 50 as the sum of two prime numbers, how many different representation methods are there (as long as the two prime numbers are the same, they are considered to be the same representation method).
将50表示为两个质数之和，不同的表示方法共有多少种(只要两个质数分别相同就认为是同一种表示方法)．
<result>4</result>