{-# OPTIONS_GHC -O2 #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE Strict #-}
{-# LANGUAGE StrictData #-}
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import Data.Array.Unboxed
import Data.Array.ST
import qualified Data.ByteString.Char8 as BS
import Control.Monad
import Data.List
import Data.Char

main :: IO ()
main = do
    (a,b,n) <- (\vec -> (vec VU.! 0, vec VU.! 1,vec VU.! 2)) . VU.unfoldrN 3 (BS.readInt . BS.dropWhile isSpace) <$> BS.getLine
    let x = min (b-1) n
    print $ (a*x)`div`b