import java.util.Scanner;

public class No_327 {
public static void main(String[] args) {
	String[] Alf = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L",
						   "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V",
						   "W", "X", "Y", "Z"};
	Scanner sc = new Scanner(System.in);
	long N = sc.nextLong();
	sc.close();
	long cal = (N / 26) - 1;
	long cal2 = N % 26;
	if(N>=26){
		System.out.print(Alf[(int) cal]);
		System.out.println(Alf[(int) cal2]);
	}else{
		System.out.println(Alf[(int) cal2]);
	}
		}
	}