A Bicycle Pump Contains Air at One Atmosphere and 0 $\degree$

A bicycle pump contains air at one atmosphere and 0 $\degree$ C. As the tyre is pumped up, the volume of air decreases by 50% with each stroke. What is the new pressure of air (in atm) in the chamber after the first stroke, assuming no temperature change?

A) 2
B) 1
C) 0.5
D) 0.1
E) 3