As its an array, the index starts from 0 (as we know) then if you wanna get the Fifth word it should be (mail.Subject.Split(" "c)(4)).ToString
Solution: Use String.Join(" ",((mail.Subject.Split(" "c)).Skip(4))) to skip the first four words from subject. It can be made dynamically if you store the value in a variable and pass it.
For Example,
In Assign activity intger strSkipCount = 4 then
pass the variable as follows, String.Join(" ",((mail.Subject.Split(" "c)).Skip(strSkipCount)))
many thanks! Unfortunately it says that this expression cannot be converted into string. But if I use .toString, it returns a meaningless code which is “System.Linq.Enuberable” in place of my desired extract.