Sharpshooters 'R' Us Gun IQ Test: Name this tune

Here's a Gun IQ test for members of Sharpshooters 'R' Us (formerly known as Gun Nutz 'R' Us, renamed due to bad publicity for admitting to being gun nuts). Name this tune being played by the Ukulele Orchestra of Great Britain. If you don't get the name right with the first three notes, you're expelled from Sharpshooters 'R' Us and you have to describe yourself as a semi-gun-nut only.