{-# LANGUAGE Safe #-}
{-# LANGUAGE PatternGuards #-}
import qualified Data.Text as T
import qualified Data.Text.IO as TI
import qualified Data.List as L
import Data.Monoid
import Data.Maybe
import Control.Applicative

(!-!)::[a]->Int->Maybe a
[] 		!-! _ = Nothing
(x:xs) 	!-! 0 = Just x
(x:xs) 	!-! n = xs !-! (n-1)

(<$~>)::Functor f => f a -> (a -> b) -> f b
(<$~>)=flip (<$>)

maybeRead s
	|[(x,"")]<-(reads s)=Just x
	|otherwise = Nothing
	
getLines::Int->IO T.Text
getLines 1 = TI.getLine 
getLines n = (<>) <$> ((<>) <$> TI.getLine <*> return (T.pack " ")) <*> (getLines$n-1)
	
run main_f n= 
	getLines n			<$~>
	T.split (==' ')		<$~>
	fmap T.unpack		<$~>
	main_f				<$~>
	fmap show			<$~>
	fromMaybe "error"	>>=
	putStrLn
	
main_ list = do
	let get n = maybeRead=<<(list !-! n)::Maybe Float
	x1<-get 0
	y1<-get 1
	x2<-get 2
	y2<-get 3
	let x_distance = x1+x2
	let y_distance = y2-y1
	return$x1/x_distance*y_distance+y1
main =	run main_ 2