Terror in London's Skies

Gloomy sky over London suddenly clouded cloud of flying flocks of birds, they would be safe if their number does not exceed the limit. A special laser gun, guarding the sky over the city at your disposal, straightens with feathered aggressors, their number increases, and it threatens a catastrophe. The gun moves from left to right 180 degrees at the same speed, your task - to include a killer beam when it is necessary to destroy a maximum of birds.