N = int(input())
S = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
s = ""

c = 1
while N >= 26**c:
    N = N - 26**c
    c += 1
    
for _ in range(c):
    N ,i = divmod(N, 26)
    s += S[i]

print(s[::-1])