#include <stdio.h>
void main(void){
	int n = 0 ,sum = 0;
	int input = scanf("%d",&n);
	if(input == 2){
		printf("入力エラー\n");
	}
	for(int i = 1 ; i <= n ; i++ ){
		sum += i;
	}
    printf("%d",sum);

}