main = do
  getLine >>= putStrLn . compute . read

compute :: Integer -> String
compute n = reverse $ take (length bs) $ loop n2
  where
    n1 = pred n
    bs = takeWhile (n >=) bases 
    n2 = n1 - sum bs

bases = 0 : iterate (26 *) 26
{- 0から25までは1桁、そこから26^2までは2桁、となる -}

loop n = ['a'..'z'] !! fromIntegral q : loop p
  where (p,q) = divMod n 26
