n = int(input())
alp = [chr(i) for i in range(65, 65+26)]

digit = 1
origin = 0
while True:
    if origin <= n < origin + 26**digit:
        break

    origin += 26**digit
    digit += 1

m = n - origin
ans = ""
for i in range(digit):
    a = m % 26
    ans = alp[a] + ans
    m //= 26

print(ans)