n = int(input())

i = 1
temp = 0
while temp <= n:
    temp += pow(26, i)
    i += 1
temp -= pow(26, i-1)
R = n-temp

res = []
for k in range(i-1):
    q, r = divmod(R, 26)
    res.append(chr(r+ord('A')))
    R = q
res.reverse()
res = ''.join(res)
print(res)