20250507
# def f(a):
# q = []
# for i in range(1, int(a)+1):
# if (a / i) % 1 == 0 :
# q.append(i)
# return len(q)
# n = float(input())
# print(f(n))
# def switch(a):
# arr = list(map(int,str(a)))
# arr.reverse()
# return ''.join(map(str,arr))
# n = int(input())
# print(switch(n))
# def sum1(a):
# a = list(map(int,str(a)))
# x = sum(a)
# a = x
# while x // 10 != 0:
# a = list(map(int,str(a)))
# x = sum(a)
# a = x
# return x
# n = int(input())
# print(sum1(n))
# def generator(a):
# a1 = list(map(int,str(a)))
# return sum(a1) + a
# a,b = map(int,input().split())
# x = 0
# q = []
# w = []
# for i in range(5100):
# q.append(i)
# for i in range(b+1):
# w.append(generator(i))
# w1 = list(set(w))
# for i in range(len(w1)):
# q.pop(q.index(w1[i]))
# for i in range(len(q)):
# if a <= q[i] <= b :
# x += q[i]
# print(x)
# Recursion
# def pid(k):
# if k == 0:
# return;
# print(k)
# pid(k-1)
# pid(100000)
# def f(k):
# if k == 0:
# return;
# f(k-1)
# print(k)
# n = int(input())
# f(n)
# def pid(k):
# if k == 0:
# return;
# print(k)
# pid(k-1)
# n =int(input())
# pid(n)
# def finder(k,r):
# if k > r:
# return;
# if k % 2 == 0:
# finder(k+1,r)
# else:
# print(k)
# finder(k+2,r)
# a,b = map(int,input().split())
# finder(a,b)
k = int(input())
def sum1(k):
if k == 0:
return;
q.append(k)
sum1(k-1)
print(sum(q))