fun main() {
    var n = readLine()!!.toLong() - 1L
    var pow = 1L
    for (e in 1..115) {
        pow *= 26L
        if (n < pow) {
            var answer = ""
            for (f in 1..e) {
                answer = ('a' + (n % 26L).toInt()) + answer
                n /= 26L
            }
            println(answer)
            return
        } else {
            n -= pow
        }
    }
}