#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
const double ERROR = 1e-11;

double theFunction(double x)
{
	x/=20;
	return ((((x+2)*x-52)*x+3)*x+524)*x-329;
}

double getX(double low,double high,double target)
{
	double slope=theFunction(high)-theFunction(low);	//for slope sign
	double x=high;
	double y=theFunction(x);
	double prev=x;
	while (fabs(theFunction(x)-target)>ERROR)
	{
		x=(high+low)*0.5;
		y=theFunction(x);

		if (prev==y) break;	//found the thing!  maybe

		if (y<target && slope>0 || y>target && slope<0) low=x;
		else high=x;

		prev=y;
	}

	return x;
}


int main()
{
	double low,high,target;
	cout.fill('0');
	while (cin>>low>>high>>target && (low!=0 || high!=0 || target!=0))
	{
		double x=getX(low,high,target);

		if (fabs(theFunction(x)-target)>ERROR) cout<<"Professor, there is no Function...\n";
		else cout<<fixed<<setprecision(4)<<x<<endl;
	}
	return 0;
}