import math
n=int(input())
alf=[chr(i) for i in range(65, 65+26)]
t=math.ceil(math.log(25*(n+1)/26+1,26))
T=n-26*(pow(26,t-1)-1)//25
ans=''
for i in range(1,t+1):
    r=pow(26,t-i)
    ans+=alf[T//r]
    T%=r
    
print(ans)