As mentioned, if you want to use a built in function then
Fix is for you.

From MSDN:
Returns the integer portion of a number.

Syntax

Int(number)

Fix(number)

The required number argument is a Double or any valid numeric expression. If number contains Null, Null is returned.

Remarks

Both Int and Fix remove the fractional part of number and return the resulting integer value.

The difference between Int and Fix is that if number is negative, Int returns the first negative integer less than or equal to number, whereas Fix returns the first negative integer greater than or equal to number. For example, Int converts -8.4 to -9, and Fix converts -8.4 to -8.

Fix(number) is equivalent to:

Sgn(number) * Int(Abs(number))