n = gets.to_i
b26 = 26
d = 0
count = 1
while true do
    p26 = b26 ** count
    break if d + p26 > n
    d += p26
    count += 1
end
k = n - d
res = k.to_s(b26)
res.length.times do |i|
    if res[i] >= "0" && res[i] <= "9"
        res[i] = ("A".ord + res[i].to_i).chr
    else
        res[i] = ("K".ord + res[i].ord - "a".ord).chr
    end
end
(count - res.length).times do
    res = "A" + res
end
puts res