import java.util.*;

class Sum{
    public int Cal(int s){
        int gokei = 0;
        for(int i=1;i<=s;i++){
            gokei = gokei + i;
        }
        return gokei;
    }
}

public class Main{
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        Sum sm = new Sum();
        int sum = sm.Cal(N);
        System.out.println(sum);
    }
}