#include<bits/stdc++.h>
using namespace std;
int f(int n)
{
    int r,b=0;
    if(n==1)
    {
        r = 1;
        b+=r;
    }
    else
    {
        r = f(n-1)+n;
    }
    return r;
}
int main()
{
    int n;
    cin>>n;
    cout<<f(n);
}
/**************************************************************
	Problem: 1148
	User: wuyichen
	Language: C++
	Result: Wrong Answer
****************************************************************/