#奇数加，偶数减
a=int(input())
b=0
for x in range(1,a+1):
    if x%2 != 0:
        b+=x
    else:
        b-=x
print(b)
'''
n = int(input())
ji = 0
ou = 0
for i in range(1, n+1):
    if i % 2 == 0:
        ou += i
    else:
        ji += i 
print(ji-ou)
'''