#include <stdio.h>
#include <math.h>
#include <assert.h>


double f(double x)
{
	if (!(-7 <= x && x <= 7))
		return nan("");
	if (x < 2) {
		if (x <= -2)
			return -0.8 * (7 + x);
		else
			return -4 - sqrt((2 - x) * (2 + x));
	} else {
		if (x <= 5)
			return -4.0;
		else
			return 3 * (x - 6) - 1;
	}
}

int main()
{
	double x = 0;
	int st = scanf("%lf", &x);
	assert (st == 1);
	double y = f(x);
	printf("f(%.16f) = %.16f\n", x, y);
	return 0;
}