N=io.read"*n"
i=1
s=0
while true do
	s=s+26^i
	if(N<s)then break end
	i=i+1
end
s=N-s+26^i-1
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))