#include<stdio.h>
int getn(int n){
	if(n==1){
		return 1;
	}else{
		return getn(n-1)+n;
	}
}
int main(){
	int i,n,s=0;
	scanf("%d",&n);
	for(i=1;i<=n;i++){
		s=s+getn(i);
	} 
	printf("%d",s);
	return 0;
}
/**************************************************************
	Problem: 1148
	User: admin
	Language: C
	Result: Accepted
	Time:16 ms
	Memory:1144 kb
****************************************************************/