#include<iostream>
#include<math.h>
double(*func)(double, double, int);
double integral_pr(double x, double y, int dx);
double integral_sim(double x, double y, int dx);
double integral_tr(double x, double y, int dx);
void main(void)
{
	double spr, str, ssim, x, y, n;
	int dx, c;
	scanf_s("%lf%lf%d", &x, &y, &dx);
	scanf_s("%d", &c);
	switch (c)
	{
	case 1:
	{
		func = &integral_pr;
		break;
	}
	case 2:
	{
		func = &integral_sim;

		break;
	}

	case 3:
	{
		func = &integral_tr;
		break;
	}

	default: {printf("Error"); }
	}
	spr = func(x, y, dx);
	printf("Result:\n s=%lf", spr);
	getchar();
	getchar();
}
double integral_pr(double x, double y, int dx)
{
	double s, x1, b;
	s = 0;
	b = (y - x) / dx;
	for (x1 = x; x1 < y; x1 = b + x1)
		s += x1*x1 * 2 + 1;
	return s*b;
}
double integral_tr(double x, double y, int dx)
{
	double s, x1, b;
	s = 0;
	b = (y - x) / dx;
	for (x1 = x; x1 < y; x1 = b + x1)
		s += (x1*x1 * 2 + 1) + ((x1 + b)*(x1 + b) * 2 + 1);
	return s*b / 2;
}
double integral_sim(double x, double y, int dx)
{
	double s, x1, b;
	s = 0;
	b = (y - x) / dx;
	for (x1 = x; x1 < y; x1 = b + x1)
		s += x1*x1 * 2 + 1 + 4 * ((x1 + b / 2)*(x1 + b / 2) * 2 + 1) + ((x1 + b)*(x1 + b) * 2 + 1);
	return s*b / 6;
}