n = input()
def souwa(n):
	if int(n[-1])%2 == 0:
		n_int = int(n)
		n_total = n_int*(n_int-n_int//2)+n_int//2
		print(n_total)
	else:
		n_int = int(n)
		n_total = n_int*(n_int-n_int//2)
		print(n_total)
souwa(n)