Players use melee attacks to fight enemies,[d] and may run, jump, swim or use vehicles to navigate the world.[e] To accommodate the map's size, the game introduces vehicle types absent in its predecessor Grand Theft Auto IV, such as fixed-wing aircraft.[11] In combat, auto-aim and a cover system may be used as assistance against enemies.[12] Should players take damage, their health meter will gradually regenerate to its halfway point.[f] Players respawn at hospitals when their health depletes.[10] If players commit crimes, law enforcement agencies may respond as indicated by a "wanted" meter in the head-up display (HUD).[13] Stars displayed on the meter indicate the current wanted level (for example, at the maximum five-star level, police helicopters and SWAT teams swarm to lethally dispatch players).[14][g] Law enforcement officers will search for players who leave the wanted vicinity. The meter enters a cool-down mode and eventually recedes when players are hidden from the officers' line of sight that displays on the mini-map for a period of time.[16][h]