import element.*;

public class SumUp
{
    public static void main(String args[])
    {
        int n, sum;
        ConsoleWindow c = new ConsoleWindow();

        sum = 0;
        n = c.input.readInt();
        sumUp(n,sum);
        c.out.println(sum);
    }

    public static void sumUp(int n, int total)
    // pre: total is zero
    // post: total is the sum of integers 1 through n
    {
        int i;
        for (i = 1; i <= n;  i++)
        {
            total += i;
        }
    }
}