In Lake Swan, there are black swans and white swans, a total of 16. Among them, the number of young swans is greater than that of adult swans. The relationship of the number of swans is: 0< Adult White Swans < Young White Swans < Young Black Swans < Adult Black Swans. The number of young black swans is .
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.