PHP, 16 bytes
$argn/sqrt(2)|0;
Try it online! (with highest value supported on TIO)
Uses @Niphram's truncate method (which in PHP also has the ability to convert the float to an int)
I know it's trendy to say PHP is to be hated, but I kinda came to like its oddities, and it gives me a chance to add an original answer
EDIT: saved 4 bytes using <?= php tag (no need to echo)
Kaddath
- 2.9k
- 5
- 9