Which of these national flags has the fewest number of stars?

The Azerbaijan flag only has one star, the Australian flag has six stars, the Bosnia and Herzegovina flag has seven full stars and two half stars, and the New Zealand flag has four stars.

The flag of Azerbaijan is a horizontal tricolour featuring three equally sized fesses of blue, red, and green, with a white crescent and an eight-pointed star in the center. The blue symbolizes Azerbaijan's Turkic heritage, the red stands for progress, and the green represents Islam. The official colors and size were adopted on February 5, 1991.

The flag of Australia is a defaced Blue Ensign: a blue field with the Union Jack in the canton (upper hoist quarter), and a large white seven-pointed star known as the Commonwealth Star in the lower hoist quarter. The fly contains a representation of the Southern Cross constellation, made up of five white stars – one small five-pointed star and four, larger, seven-pointed stars.

The national flag of Bosnia and Herzegovina contains a wide medium blue vertical band on the fly side with a yellow right triangle abutting the band and the top of the flag. The remainder of the flag is medium blue with seven full five-pointed white stars and two half stars top and bottom along the hypotenuse of the triangle.

The flag of New Zealand is a defaced Blue Ensign with the Union Flag in the canton, and four red stars with white borders to the right. The stars' pattern represents the asterism within the constellation of Crux, the Southern Cross.