formula help please

Hope some out there can lend me a hand. Having problems with C1 can be a % or can also be an amount. Every entry can vary
here goes.
A1 contains buy in price €
B1 contains discount €, it varies but is always a figure in €
C1 Contains another discount in € OR it may contain a % discount based on the buy in price.
D1 is to contain the sellout price based on A1,B1,C1.

The % discount varies with product.
Any help out there with a formula for D1