import Data.Array((!), listArray, Array, bounds)
import Data.List(sort)

pickMedian :: Array Int Double -> Double
pickMedian xs = (xs ! mid + xs ! mid2) / 2
    where
        (start, end) = bounds xs
        mid = (end) `div` 2
        mid2 = if mod mid 2 == 1
            then mid
            else (end + 1) `div` 2

median xs = pickMedian $ listArray (0, length xs - 1) (sort xs)

readInt :: String -> Double
readInt = read

main = getLine >>= print . median . map readInt . words