@David_Phillips I would highly suggest going with a regex solution instead of the IndexOf solution, as it is much more versatile. The existing IndexOf solution would not work if there were additional digits, less digits, or changes in the spaces between success and the number you want.
With Regex you could just use the Read Text File activity, save it to a string variable, then do a simple regex to pull out the information you want.expression:
(?<=\bSUCCESS\s*)\d+ and make sure regex options Ignore Case is checked. You could do this with the Matches activity, or you could do it in an assign activity
This would match the word success anywhere in the text document and pull out the number immediately to the right of it. I suggest you give it a try here: http://regexstorm.net/tester and use the reference page here for any future regex help http://regexstorm.net/reference
EDIT: How the expression works: (?<=) means that it will search for the pattern you put, and grab the text immediately to the right. \b grabs a word boundary. Success is the literal word success, and \s* means it will grab 0 or more whitespaces after the word success. All together (?<=\bSUCCESS\s*) is looking for the word success by itself, followed by 0 or more white spaces. So it won’t match the word successful, and it won’t match unsuccess. After it finds success, it looks to the pattern to the right which is \d+. This means it is finding 1 or more digits. Put the whole thing together (?<=\bSUCCESS\s*)\d+ and you are finding one more digits immediately after the word success within the string you are searching