import Control.Monad
main = do
  n <- readLn
  let m = if n > 26^10+26^9+26^8+26^7+26^6+26^5+26^4+26^3+26^2+26
          then 11
          else if n > 26^9+26^8+26^7+26^6+26^5+26^4+26^3+26^2+26  
               then 20
               else if n > 26^8+26^7+26^6+26^5+26^4+26^3+26^2+26
                    then 9
                    else if n > 26^7+26^6+26^5+26^4+26^3+26^2+26
                         then 8
                         else if n > 26^6+26^5+26^4+26^3+26^2+26    
                              then 7
                              else if n > 26^5+26^4+26^3+26^2+26
                                   then 6
                                   else if n > 26^4+26^3+26^2+26
                                        then 5
                                        else if n > 26^3+26^2+26
                                             then 4
                                             else if n > 26^2+26
                                                  then 3
                                                  else if n > 26
                                                       then 2
                                                       else 1
                                                          

  let l = if n > 146813779479510
          then n-146813779479510
          else if n > 5646683826134
               then n-5646683826134
               else if n > 217180147158
                    then n-217180147158
                    else if n > 8353082582
                         then n-8353082582
                         else if n > 321272406
                              then n-321272406
                              else if n > 12356630
                                   then n-12356630
                                   else if n > 475254
                                        then n-475254
                                        else if n > 18278
                                             then n-18278
                                             else if n > 702
                                                  then n - 702
                                                  else if n > 26
                                                       then n - 26
                                                       else n
  putStrLn $ solve l m

solve l m = (replicateM m ['a'..'z']) !! (l-1)
