/*****
      y_480.c
      2017.6.22 Saho Igami
*****/

#include <stdio.h>

int main() {
    int num;
    int sum = 0;
    int i;

    printf("input number: ");
    scanf("%d", &num);
    
    for(i = 0; i <= num; i++) {
        sum = sum + i;
    }
    printf("%d\n", sum);
    return 0;
}