N=io.read"*n"
i=1
s=0
while true do
	s=s+math.floor(26^i+.5)
	if(N<s)then break end
	i=i+1
end
s=N-s+math.floor(26^i+.5)-1
if(s<0)then i=i-1 s=math.floor(26^i+.5)-1 end
r={}
ab=string.byte"a"
for j=1,i do
	r[i-j+1]=string.char(ab+s%26)
	s=(s-s%26)/26
end
print(table.concat(r))