It's not complex, there are several ways you could do it.
You could read the file as a series of lines, and find the line starting with "Assassins Creed:" (string.StartsWith will tell you that). The rest of the line is your number.
You could read the whole file as a string (File.ReadAllText will do that) and then use a Regular Expression to find the data you want:
private static Regex findIt = new Regex(
"(?<=Assasins Creed:\\s+)\\d+",
RegexOptions.Multiline
| RegexOptions.CultureInvariant
| RegexOptions.Compiled
);
...
Match m = findIt.Match(textFromTheFile);
if (m.Success)
{
string theValueYouWanted = m.Value;
...
}
Wither way, once you have the data, you can use int.TryParse to convert it to a number:
int assassinsCreedCount;
if (int.TryParse(theValueYouWanted, out assassinsCreedCount))
{
...
}