20250816

'''
 n = int(input())
 if 조건식 :
     print()
 elif 조건식 :
     pass
 else :


 6059-6064 제외
~ 6070 풀기
'''

'''
s = bool(int(input()))
print(not s)
'''
'''
s, v = input().split()
print(bool(int(s)) and bool(int(v)))
'''
'''
s, v = input().split()
print(bool(int(s)) or bool(int(v)))
'''
'''
s, v = input().split()
i = bool(int(s))
r = bool(int(v))
print((i and (not r)) or ((not i) and r))
'''
'''
s, v = input().split()
print(not bool(int(s)) and not bool(int(v)))
'''
'''
s = int(input())
print(~s)
'''
'''
s, v = map(int, input().split())
print(s & v)
'''
'''
s, v = map(int, input().split())
print(s | v)
'''
'''
s, v = map(int, input().split())
print(s ^ v)
'''
'''
s, v = map(int, input().split())
print(s if (s>=v) else v)
'''
'''
s, v, r = map(int, input().split())
print((s if s<v else v) if ((s if s<v else v)<r) else r)
'''
'''
s, v, r = map(int, input().split())
if s%2==0 :
  print(s)

if v%2==0 :
  print(v)

if r%2==0 :
  print(r)
'''
'''
s, v, r = map(int, input().split())
if s%2==0 :
  print("even")
else :
  print("odd")

if v%2==0 :
  print("even")
else :
  print("odd")

if r%2==0 :
  print("even")
else :
  print("odd")
'''
'''
s = int(input())
if s<0 :
  if s%2==0 :
    print('A')
  else :
    print('B')
else :
  if s%2==0 :
    print('C')
else :
    print('D')
'''
'''
s = int(input())
if s>=90 :
  print('A')
else :
  if s>=70 :
    print('B')
  else :
    if s>=40 :
      print('C')
    else :
      print('D')
'''
'''
s = input()
if s=='A' :
  print('best!!!')
elif s=='B' :
    print('good!!')
elif s=='C':
    print('run!')
elif s=='D' :
    print('slowly~')
else :
    print('what?')
'''
'''
s = int(input())
if s==12 or s<=2 :
  print('winter')
elif 3<=s<=5 :
    print('spring')
elif s>=6 and s<=8 :
    print('summer')
else :
    print('fall')
'''
'''
s = int(input())
if 30<=s<=40 or 60<=s<=70 :
  print('win')
else :
    print('lose')
'''
'''
s, v = map(int, input().split())
if s==90 :
    print(v)
else :
    r=(90-s)//5
    if s%10==0 :
        print(v+r)
    else :
        print(v+r+1)
'''
'''
s = int(input())
v = ((s%10*10)+(s//10))*2
if v>=100 :
    v=v-100
print(v)
if v<=50 :
    print('GOOD')
else :
    print('OH MY GOD')
'''
'''
s, v, r = map(int,input().split())
if s<v-r :
    print('advertise')
elif s>v-r :
    print('do not advertise')
else :
    print('does not matter')
'''
'''
반복문
1. for  + range
2. while

while 조건문 : 
    반복명령


range(5)        0이상     5미만     1간격     [0,1,2,3,4]
range(2,7)      2이상     7미만     1간격     [2,3,4,5,6]
range(2,7,2)    2이상     7미만     2간격     [2,4,6]

range(5,0,-1)   5이하     0초과     -1간격     [5,4,3,2,1]

break       반복문 탈출하기
continue    다음반복으로 넘어가라 
'''

# for i in range(5) :
#     print(i)
#     #i=i+2 아무의미없다!!
#
# for i in [0,1,2,3,4] :
#     print(i)
'''
s =2147483647
while s!=0 :
  s = int(input())
  if s!=0 :
    print(s)
'''
'''
s = int(input())
for i in range(s, 0, -1) :
    print(i)
'''
'''
s = int(input())
for i in range(s-1, -1, -1) :
    print(i)
'''
'''
s = ord(input())
v = ord('a')
while v<=s :
  print(chr(v), end=' ')
  v += 1
'''
'''
s = int(input())
for i in range(s+1) :
    print(i)
'''
'''
s = int(input())
for i in range(s+1) :
    print(i)
'''
s = int(input())
sum = 0
for i in range(1, s+1) :
    if i%2==0 :
        sum += i
print(sum)