#include <bits/stdc++.h>
using namespace std;
int main(){
    int a,b;
    cin>>a;
    b=(a+1)*a/2;
    cout<<b;
}
/**************************************************************
	Problem: 1002
	User: zhangyilei
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/