/*

Vassilis Athitsos
UTA ID: 

*/

#include <stdio.h>


int main( void )
{
	int number;
	int sum;
	int i;

	do
	{
		printf("please enter a number:\n");
		scanf("%d", &number);

		if (number < 0)
		{
			break;
		}

		sum = 0;

		for (i = 0; i <= number; i++)
		{
			sum = sum + i;
		}

		printf("sum of numbers from 0 to %d is %d\n\n", number, sum);
	}
	while(1);
}