#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

double fisr(double number);

int main(void) {
	double a = 2;
	//scanf("%lf", &a);
	printf("%lfn", fisr(a));

	system("pause");
	return 0;
}

double fisr(double number) {
	long i;
	float x2, y;
	const float threehalfs = 1.5F;

	x2 = number * 0.5F;
	y  = number;
	i  = * ( long * ) &y;                       // evil floating point bit level hacking
	i  = 0x5f3759df - ( i >> 1 );               // what the fuck?
	y  = * ( float * ) &i;
	y  = y * ( threehalfs + ( x2 * y * y ) );   // 1st iteration
//	y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed

	return y;
}