Shoot the zombies six times in the leg or body then knife them in the first round 
you may not be running low on ammutnition but if you do have 4 or less bullets 
left shoot them in the head at round two but if not shoot the zombie 8 times in 
the leg or body then knife them round three I just knifed them all 3 times to kill 
one or shot them in the head with my almost out ammo then knife dont open the door 
till the begining of round 5 but how to keep surviving at 4 is eather throw a 
grenade and keep knifing them or if your backed up i just eathir open the door 
and get the submachine gun or open the box (if its there).