#include <stdio.h>

int main(void){
	long long int d,n,u,tmp;
	long long int maxNum = 0;
	
	scanf("%lld", &n);
	
	for(d=0;d<=n;d++){
		u = n-d;
		tmp = (d+1)*u+d;
		if(maxNum < tmp){
			maxNum = tmp;
		}
	}
	
	printf("%lld\n", maxNum);
	return 0;
}