#include<iostream>
#include<cmath>
using namespace std;
double Q_cbrt(double number)
{
	long long i;
	double x2, y;
	const double twothird = 0.66667;
	x2 = number * 0.5;
	y = number;
	i = * (long long *) &y;   
	i = 3071319837877857280ll + i / 3;     
	y = * (double *) &i;
	y = twothird * (y + x2 / y / y);
	y = twothird * (y + x2 / y / y);
	y = twothird * (y + x2 / y / y);
	return y;
}
int main()
{
	double x;
	cin >> x;
	cout << floor(Q_cbrt(x)) << endl;
}

模仿的《雷神之锤Ⅲ》的平方反根算法。然而第7个点炸了，结果比答案大1。 多加几次牛顿迭代也没用。