Sum Problem

#include <stdio.h>

int main(void) {
    int a;
    while (scanf("%d", &a) == 1)
    {
        if (a % 2 == 0)
            printf("%d\n\n", (a / 2) * (a + 1));
        else
            printf("%d\n\n", ((a + 1) / 2) * a);
    }
}