include <stdio.h>

int main() {

int a,b=0,c,d=1,e=1;
scanf("%d",&a);
while (e<=a){
	for (int j=1;j<=d;j++){
		b=b+d;
		e++;
		if(e>a){
			break;
		}
	}
	d++;
}
printf("%d",b);

}