Converting a string to number

Good morning all, ok im trying to convert a string to a numerical value. The problem I am having is that the number has 2 dashes in it. Example and this is always the same 0500-010-95. Is there any way i can change this to a number value so i can create a grouping. The first set is the main the second set is sub-account and the third is department. I am using CR 8.5. I tried converting to a number using the ToNumber({mystringfield}) but it told me it was not a numerical value.

Thanks a lot.

Bryan
Bmcafee@.regio-tile.comTry
ToNumber(replace({mystringfield},'-',''))