k = int(input())
 
even_list = []
odd_list = []
 
is_odd = True
for j in range(1, k + 1):
    if is_odd:
        odd_list.append(j)
    else:
        even_list.append(j)
    is_odd = not is_odd
 
print(int(len(even_list) * len(odd_list)))