import string

N = int(input())
S = ''
while True:
    if N < 26:
        S += string.ascii_uppercase[N]
        break
    else:
        t = 26
        while t * 27 < N + 1:
            t *= 26
        S += (string.ascii_uppercase)[N % (t * 26) // t - 1]
        N -= N // t * t
print(S)