solve :: Integer -> Integer
solve k = ((k - 1)*(start + start + 2*(k - 1)) `quot` 2) + (start + 2*(k `quot` 2)) - if even k then 1 else 0
    where triangle n = (n*(n + 1)) `quot` 2
          start = 1 + 2*triangle (k - 1)

breakInIncrements :: [Integer] -> [[Integer]]
breakInIncrements = go 1
    where go n as = take n as : go (n + 1) (drop n as)

main :: IO ()
main = interact $ show . solve . read