#include <iostream>
#include <vector>
#include <iomanip>
#include <cmath>
using namespace std;
/*
double calc(const vector<double>& func, int x){
    int n = func.size();
    double ans = 0;
    for(int i = 0; i < n; i++){
        ans += pow(x, n-i) * func[i];
    }
    return ans;
    }*/
//秦九韶算法
double calc(const vector<double>& func, double x){
    double ans = 0;
    for(double y: func){
        ans = x * ans + y;
    }
    return ans;
}
int main(){
    int n;
    double l, r;
    n = 3; l = -0.9981; r = 0.5;
    //cin >> n >> l >> r;
    //任取两个点，把[l, r]分成三段，调整l, r的值
    vector<double> func(n+1);
    func[0] = 1; func[1] = -3; func[2] = -3; func[3] = 1;
    /*for(int i = 0; i < n; i++){
        
      }*/
    double mid1, mid2;
    double ans = 0;
    while(r - l > 1e-6){
        mid1 = l + (r-l)/3;
        mid2 = r - (r-l)/3;
        if(calc(func, mid1) > calc(func, mid2)){
            r = mid2;
        } else if(calc(func, mid1) <= calc(func, mid2)) {
            l = mid1;
        }
        
    }
    cout << fixed << setprecision(8) << l << endl;
    return 0;
}