L=[0,26]
for i in range(2,10):
    L.append(L[-1]+26**i)
#print(L)

N=int(input())
N=N

l=0
for i in range(10):
    if N>=L[i]:
        continue
    else:
        l=i
        break
#print(l)
n=N-L[l-1]
a=["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
ANS=""
for i in range(l):
    ANS+=a[n//(26**(l-1-i))]
    n%=26**(l-1-i)
print(ANS)