EXTRACTFILENAME

EXTRACTFILENAME(text, optional path_separator)
Returns only the file name from a full file path.

text	The value or cell address from which you want to extract only the file name
path_seperator	The path separator Optional, if omitted a backslash (\) is used.

REMARKS
Returns the file name from a full path and filename. By default the formula uses a backslash (\) as separator, but optionally you can specify another separator.
For example =ASAPEXTRACTFILENAME("D:\Projects\Archive\Client 1\Balance.xls") returns "Balance.xls".