n = int(input())

x = 1
while True:
    p26 = pow(26, x)
    if n < p26:
        break
    n -= p26
    x += 1

ans = ['A']*x
i = -1
while n != 0:
    ans[i] = chr(ord('A') + (n % 26))
    n //= 26
    i -= 1

print(''.join(ans))