from bisect import bisect_right

n = int(input())

N = [0]
for i in range(1, 11):
    N.append(N[-1] + pow(26, i))
ANS = ['' for _ in range(11)]
f = True
while True:
    idx = bisect_right(N, n) - 1
    if idx == 0:
        ANS[10 - idx] = chr(ord('A') + n)
        break
    res = n - N[idx]
    r = res // pow(26, idx)
    ANS[10 - idx] = chr(ord('A') + r)
    if f:
        for i in range(10 - idx + 1, 11):
            ANS[i] = 'A'
        f = False
    n -= (r + 1) * pow(26, idx)
print(''.join(ANS))