import string
N = int(input())
digit = 0
total = 0
while (total + 1) * 26 - 1 < N:
    total = (total + 1) * 26 - 1
    digit += 1
# print(digit)
S = ''
S = string.ascii_uppercase[N%26]
i = 27
N += 1
while N >= i:
    S += string.ascii_uppercase[N%(i*27)//i - 1]
    i *= 27
print(S[::-1])