D = int(raw_input())
if D < 4:
	print 0
else:
	ans = 0
	for i in range(4,D + 1):
		if i * 4 == D:
			ans = max(ans,i * (D - i * 2) / 2)
		if D > i * 2 and D % 2 == 0:
			ans = max(ans,i * (D - i * 2)/2)
		if D > i * 2 and D % 2 == 1:
			ans = max(ans,i * ((D - 1) - i * 2)/2)
	print ans