import sys
import math

d = int(input())
if d < 4:
    print(0)
    sys.exit()
    
if d % 2 == 1:
    d -= 1

if d % 4 == 0:
    ans = pow(d / 4,2)
else:
    a = int(math.sqrt(d))
    ans = a * (a + 1)

print(int(ans))