#include<stdio.h>
int main(){
int main(){
int n;}
while(scanf("%d",&n),n>0) printf("%d\n\n",n%2?(n+1)/2*n:n/2*(n+1));
return 0;
int n;}
while(scanf("%d",&n),n>0) printf("%d\n\n",n%2?(n+1)/2*n:n/2*(n+1));
return 0;