#include <iostream>
using namespace std;
int main ()
{
    int n,s=0;
    cin>>n;
    if (n>0 )
    {
    for (int i=0;i<=n;i++)
        s=s+i;

        cout<<s<<endl;}
    else
        if (n<=0)
    {    for (int i=n;i<=1;i++)
            s=s+i;
    cout<<s<<endl;
    }
    return 0;
}