def func(value, k, keta) -> str:
    ans = []
    if value == 0:
        ans.append('A')
    while value != 0:
        ans.append(chr(65 + (value%k)))
        value = value // k
    ans.reverse()
    return ''.join(ans).rjust(keta, 'A')

N = int(input())

tot = 0
keta = -1
for i in range(1, 10):
    tot += 26**i

    if tot > N:
        keta = i
        sofar = tot - 26**i
        break

ans = func(N - sofar, 26, keta)
print(ans)