#include <cstdio>

int main(){
	int i,n,sum;
 
	scanf("%d",&n);
	sum=0;
	i=1;
	while (i<=n){
		sum=sum+i;
		i=i+1;
	}
	printf("%d\n",sum);
	
	int pause;
	scanf("%d",&pause);
	return 0;   
}