#include <stdio.h>
#include <math.h>
double x,x1,x2;
double fx(double x)
{
	double c;
	c=x*x*x-5*x*x+16*x-80;
	return(c);
}

double root(double x1,double x2)
{
	do{
	double k,b;
	k=(fx(x1)-fx(x2))/(x1-x2);
	b=fx(x1)-k*x1;
	x=-b/k;
	if(fx(x)*fx(x1)>=0)x1=x;
	if(fx(x)*fx(x2)>=0)x2=x;}
	while(fx(x)<-0.00001||fx(x)>0.00001);
}

int main()
{
	while(fx(x1)*fx(x2)>=0)
	{
		scanf("%lf%lf",&x1,&x2);
	}
	root(x1,x2);
	printf("%f",x);
	return 0;
}