import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

N = int(read())

full = [26 ** n for n in range(10)]
full[0] = 0

n = 0
while True:
    if sum(full[:n+1]) < N+1:
        n += 1
        continue
    break

N = N - sum(full[:n])

# n桁のN番目

A = []
for _ in range(n):
    N,r = divmod(N,26)
    A.append(r)

answer = ''.join(chr(x + ord('A')) for x in A[::-1])
print(answer)