import Control.Applicative( (<$>))

main = do
    [n_, a_, b_] <- map (read::String->Integer) . words <$> getLine
    let
	combi n r = let
			numerator = product [n-r+1..n]
			denominator = product [1..r]
		    in
			numerator `quot` denominator

    print $ if a_>b_ || (a_<b_&&n_==1)
		then 0
		else combi (b_-a_+n_-2) (n_-2)