using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    public void Solve()
    {
        int N = int.Parse(Console.ReadLine());

        int sum = 0;
        for (int i = 1; i <= N; i++) { sum += i; }
        Console.WriteLine(sum);
    }

    static void Main()
    {
        var solver = new Program();
        solver.Solve();
    }
}