Selecting half the elements with :nth-child?

[Maragenie]

Take the following code for instance:\[code\]<ul> <li>Hello World</li> <li>Hello World</li> <li>Hello World</li> <li>Hello World</li></ul>\[/code\]Is it possible, using \[code\]:nth-child()\[/code\] or otherwise, to select exactly half of the total elements? The code should select the first/last two \[code\]li\[/code\]s in the above instance, then if I were to increase the number of \[code\]li\[/code\]s to six, it would select the first/last three.I feel I'm going to have to use JavaScript...