The city is teeming with monsters, and where they came from is unknown. Perhaps they descended from the mountains or climbed out of the ground. It really doesn't matter. You need to quickly find a weapon and survive.
Control keys:
F - Pick up weapons, ammo
1,2,3 ... Change weapons
WASD - Character movement
SPACEBAR - Jump
SHIFT - Sprint
Esc - Exit to the menu
LKM - Shoot