#include <stdio.h>
#include <locale.h>
#include <math.h>
#include <stdlib.h>

int progr(float a, float d, int n, float* n_element, float* sum);
int main(void)
{
float a, d, n_element, sum;
int n;
	int st;
	printf("input a, d, n \n");
scanf("%f %f %d", &a, &d, &n);

	st=progr(a, d, n, &n_element, &sum);
	switch(st)
	{

		case 0: printf("vse horosho\n"); break;
		case 3: printf("n<0\n"); break;
		case 100: printf("all elements are equals\n"); break;
		case 5: printf("different sgn\n"); break;
	};
	printf("n_element = %f, summa = %f", n_element, sum);
	return 0;
};

int progr(float a, float d, int n, float* n_element, float* sum)
{
	if (n<0) return 3;
	float s = a;
	float an = a;
	for(int i = 2; i<=n; i++)
	{
		an = an + d;
		s = s + an;
	}
	*n_element = an;
	*sum = s;


	if (s == a*n) return 100;
	if ((a<0&&an>=0)||(a>=0&&an<0)) return 5;
 return 0;

}