根据下述要求，编写一个程序：用户输入一个字符串，将下标为偶数的字符提出来合并成一个新的字符串A，再将下标为奇数的字符提出来合并成一个新的字符串B，再将字符串A和B连接起来并输出。

rs = []
even = ""
odd = ""
rastr = input("请随意输入一个字符串:")
for string in rastr:rs.append(string)
for estr in (rastr[::2]):even = even + estr
for ostr in (rastr[1::2]):odd = odd + ostr
A = even + odd
print(A)