If the sum of a range is equal to or less than the sum

[avidcat]

I need help creating a formula for the following cell A4.

If the sum of A1,A2 & A3 is 3 then A4 will show the sum of 1.

If the sum of A1,A2 & A3 is less than 3 then A4 will show the sum of 0.

Thanks for any help.

Nick