n = int(input())

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

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

print(''.join(ans))