#include <stdio.h>
#include <stdlib.h>
#include <string.h>



int sum_to_n(int n) {
    // TODO: implement this recursively
    return 0;
}


int main(void) {
    int n;
    if (scanf("%d", &n) != 1) { n = 0; }
    printf("%d\n", sum_to_n(n));
    return 0;
}