main = do
 [xa,ya] <- map read . words <$> getLine
 [xb,yb] <- map read . words <$> getLine
 print (saitama (xa,ya) (xb,yb))

saitama pa@(xa,ya) pb@(xb,yb) = (yb-ya) * ratio + ya
 where ratio = xa / (xa+xb)