Given the strings s1 and s2, not necessarily of the same length, create a new string consisting of alternating characters of s1
and s2 (that is, the first character of s1 followed by the first character of s2, followed by the second character of s1, followed by the second character of s2, and so on. Once the end of either string is reached, no additional characters are added. For example, if s1 contained "abc" and s2 contained "uvwxyz", then the new string should contain "aubvcw". Assign the new string to the variable s3.
