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

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