#include<bits/stdc++.h> using namespace std; int main() { int n;cin>>n; cout< a1, a2, a3..... an an,an-1,an-2.....a1 (a1+an)*n/2=(1+n)*n/2

N = int(input())
"""
numList = list(range(1,N+1))
print(sum(numList))
"""
s = 0 
for i in range(1,N+1):
    s+=i
print(s)