import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Read as T

main :: IO ()
main = do
  [a, b, n] <- map unsafeTextToInt . T.words <$> T.getLine :: IO [Int]
  print $ a * min (pred b) n `div` b

unsafeTextToInt :: T.Text -> Int
unsafeTextToInt s = case T.signed T.decimal s of
  Right (n, _) -> n
