N = int(input())
al = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
res = 0
for i in range(1, 10):
    res += 26**i
    if res >= N:
        break
r = i
ans = ''
N -= (res - 26**r)
for j in range(r):
    if j == r-1:
        ans += al[N]
    else:
        a, N = N//(26**(r-j-1)), N%(26**(r-j-1))
        ans += al[a]
print(ans)