Given the strings $s1$ and $s2$ that are of the same length, create a new string consisting of the first character of s$1$ followed by the first character of $s2,$ followed by the second character of $s1,$ followed by the second character of $s2,$ and so on $($in other words the new string should consist of alternating characters of $s1$ and $s2).$ For example, if $51$ contained "hello" and $s2$ contained "world", then the new string should contain "hweolrllod". Assign the new string to the variable $s3.$