#include <bits/stdc++.h>
using namespace std;
//返回 1+2+3+...+(x-1)+x
int f(int x)
{
    if (x == 1)
        return 1;
    return f(x - 1) + x;
}
int main()
{
    int n;
    cin >> n;
    cout << f(n) << "\n";
    return 0;
}