import Control.Applicative

main :: IO ()
main = do
    [n, a, b] <- (map read . words) <$> getLine
    print $ mod (2 ^ n - 1 - choose n a - choose n b) (10 ^ 9 + 7)

choose :: Integer -> Integer -> Integer
choose n k = div (product [n, n - 1 .. n - k + 1]) (product [1 .. k])
