import java.util.Scanner;
public class bt7TongN{

    public static int nhapInt(){
    Scanner n=new Scanner(System.in);
    boolean check =false;
    int a=0;
    while(!check){
        try{
            a=n.nextInt();
            if (a>0){
                check=true;
            }else{
                System.out.println("Du lieu vao khong dung, nhap lai: ");
            }
        }catch(Exception e){
            System.out.println("Du lieu vao khong dung, nhap lai: ");
            n.nextLine();
        }
    }
    return(a);
}
    public static void main(String[] args)
    {
        int n=0,s=0;
        System.out.print("Nhap vao gia tri n (nguyen): ");
        n=nhapInt();
        for(int i=1;i<=n;i++)
        s=s+i;
        System.out.println("Tong tu 1 den "+n+" la: "+s);


    }
}