using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp3 {
    class Program {
        static void Main(string[] args) {
            var scanner = new Scanner();

            int N = scanner.NextInt();
            int sum = 0;

            for (int i = 1; i <= N; i++) {
                sum += i;
            }

            Console.WriteLine(sum);
        }
    }

    class Scanner {
        int index = 0;
        string[] tokens = { };

        public string Next() {
            if (index == tokens.Length) {
                index = 0;
                tokens = Console.ReadLine().Split(' ');
            }
            return tokens[index++];
        }

        public int NextInt() {
            return int.Parse(Next());
        }

        public long NextLong() {
            return long.Parse(Next());
        }
    }
}