Keg, 6 bytes
21½Ë/ℤ This defines the function f as:
- Taking a single parameter, then
- Calculating the square root of 2 by raising it to the power of 0.5, then
- Dividing the parameter by root 2, then
- Casting the result to an integer (truncating / flooring the result) and returning it.
The footer is to define the test cases in a nice way.