HDU 1001

#include <stdio.h>
int main(void)
{
        int n;
        int i = 0;
        while(1)
        {
                if(scanf("%d", &n) != EOF) {
                        /*
                        if(i != 0)
                                printf("\n");
                        i++;
                        */
                } 
                else
                        break;
                if(n % 2)
                        printf("%d\n\n", (n + 1) / 2 * n);
                else
                        
                        printf("%d\n\n", n / 2 * (n + 1));
        }
        return 0;       
}