Even though "hek at theeks dot net"'s answer is valid, I would not recommend using the abs() hack recommended. Even though it is by far the most common, not all languages treat (n != 1) as plural. Other languages are much more complex, for example, here is how you determine plurals in Macedonian.
n==1 || n%10==1 ? 0 : 1
In Arabic there are actually 5 different types of plurals:
n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 : n%100>=11 ? 4 : 5
If you are using only specific languages that use the (n != 1) format AND -1 is singular, by all means, use abs(), but be careful and don't forget that you have done this when adding a new language to your project 3 years down the road.
