n = int(input())
x = n // 2
m = []
for i in range(1, x + 1):
    for j in range(1, x + 1):
        if((i + j) * 2 == n):
            z = i * j
            m.append(z)
print(max(m))
/**************************************************************
	Problem: 1356
	User: admin
	Language: Python
	Result: Accepted
	Time:94 ms
	Memory:34480 kb
****************************************************************/