#include <stdio.h>
#define WriteLine() printf("\n");
#define WriteLong(x) printf(" %lld", x);
#define ReadLong(a) if (fscanf(stdin, "%lld", &a) != 1) a = 0;
#define long long long

void loop_0(long a)
{
    long i;
    long sum;
    i = 0;
    sum = 0;
    while (i < a) {
        sum = sum + i;
        i = i + 1;
    }
    WriteLong(sum);
}