A gaseous mixture of two substances A and B, under a total pressure of \( 0.8 \, \text{atm} \) is in equilibrium with an ideal liquid solution. The mole fraction of substance A is \( 0.5 \) in the vapour phase and \( 0.2 \) in the liquid phase. The vapour pressure of pure liquid A is __________ \( \text{atm} \). (Nearest integer)