n=input()
if n<1:print'a';exit()
a,f=0,1
while n>1:a,f,n=f,a+f,n-1
r=''
while f:r,f=chr(f%26+97)+r,f//26
print r
bj1pbnB1dCgpCmlmIG48MTpwcmludCdhJztleGl0KCkKYSxmPTAsMQp3aGlsZSBuPjE6YSxmLG49ZixhK2Ysbi0xCnI9JycKd2hpbGUgZjpyLGY9Y2hyKGYlMjYrOTcpK3IsZi8vMjYKcHJpbnQgcg==