n = int(input()) + 1

alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
tmp = [26 ** i for i in range(1, 20)]
lst = [0]
for num in tmp:
    lst.append(lst[-1] + num)
for i, num in enumerate(lst):
    if num >= n:
        p = i
        break
ans = list("A" * p)
n -= lst[p - 1] + 1
for i in range(p - 1, -1, -1):
    if n == 0:
        break
    pos = n % 26
    n //= 26
    ans[i] = alpha[pos]
print("".join(ans))