N = int(input())
txt  = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

c = [0]*9
for rank in range(10):
	N -= 26**(rank+1) 
	if N < 0:
		N += 26**(rank+1)
		break
for i in range(rank,-1,-1):
	p = N/(26**i)
	c[i] = p
	N -= p*(26**i)
print "".join([txt[c[j]] for j in range(rank,-1,-1)])