N = int(input())
d = 1
for i in range(1, 100):
    if N >= 26 ** i:
        d = i + 1
        N -= 26 ** i
    else:
        break

ans = []
for i in range(d):
    ans.append( chr((N % 26 + ord("A"))) )
    N //= 26
ans.reverse()
print(*ans, sep="")