{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE BinaryLiterals #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE NumDecimals #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}

import Control.Applicative
import Control.Arrow
import Control.Monad
import Control.Monad.ST

import Data.Char
import Data.List
import Data.Maybe

import qualified Data.ByteString.Char8 as B

import Data.Array.ST.Safe
import Data.STRef

import Debug.Trace
import Text.Printf

readInt = readLn :: IO Int
readInteger = readLn :: IO Integer
readInts = map ( fst . fromJust . B.readInt ) . B.words <$> B.getLine
readIntegers = map ( fst . fromJust . B.readInteger ) . B.words <$> B.getLine

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

modifyArray a i f = writeArray a i =<< f <$> readArray a i

main = do
	[ a, b, h, m ] :: [Double] <- map fromIntegral <$> readInts
	let
		theta1 = ( h / 12 + m / 60 / 12 ) * pi * 2
		theta2 = m / 60 * pi * 2
		y1 = a * sin theta1
		x1 = a * cos theta1
		y2 = b * sin theta2
		x2 = b * cos theta2
		d = sqrt $ ( y1 - y2 ) ^ 2 + ( x1 - x2 ) ^ 2
	printf "%.12f\n" d