https://www.acmicpc.net/problem/8393
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int answer = 0;
for(int i = 1; i <= n; i ++){
answer += i;
}
sc.close();
System.out.println(answer);
}
}