let genWord  = 
    let cnt = ref 1    
    (fun (preWord:string) ->
        let preWord = preWord.ToCharArray()
        let preLastCharacter = preWord |> Array.last
        let addWord = (('a' |> int) + cnt.Value) |> char
        incr cnt
        let newWord = new string[|preLastCharacter;addWord|] 
        newWord)    

let startWord = "aa"

let n = stdin.ReadLine() |> int

startWord
|> Seq.unfold(fun word -> 
    let newWord = genWord word
    Some(word,newWord))
|> Seq.take n
|> Seq.iter(printfn "%s")