How can a Integer Amount field be made to read '0' for any negative values

Scenario : A(Currency Amount) * B(Integer Amount) = C(Currency Amount)  [e.g. Rate * Days = Amt]

where B(Integer Amount) is a formula = (Date Field) - (Today Date/Time) [Difference between two date pickers]

We donot want, C to show negative values.We have restrcited A from not holding negative values.B however is a difference b/w two dates which can be a turn negative.What we are trying to, is to set this to '0' if the difference turns negative