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

int main(void)
{
	double x, y;

	scanf("%lf", &x);
	y = rt3(x);
	printf("%f\n", y);

	return 0;
}

double rt3(double a)
{
	double x, new_x;

	x = a;

	while (1) {
		new_x = x - (x*x*x - a) / (3*x*x);
		if (fabs(new_x - x) < 1e-10) break;
		x = new_x;
	}

	return new_x;
}