#define _USE_MATH_DEFINES
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

double find(double x, double eps, int c)
{
	double t = (double) c;
  	double f, df;
  	do {
    	f = x * x + x + sqrt(x) - t;
    	df = 2*x + 1 + 0.5 / sqrt(x);
    	x = x - f / df;
  	} while (fabs(f) > eps);
  	return x;
}

int main()
{
	int c;
	cin >> c;
  	cout << fixed << setprecision(7) << find(0.5, 0.0000001, c);
  	return 0;
}