#include<bits/stdc++.h>
using namespace std;
int a,c,b;
int main(){
    cin>>a;
    for(int i=1;i<=a;i++){
        c=c+i;
           
    } 
    cout<<c;
    }
/**************************************************************
	Problem: 1002
	User: suziqian
	Language: C++
	Result: Accepted
	Time:44 ms
	Memory:2072 kb
****************************************************************/