数的三次方根

#include <bits/stdc++.h>
using namespace std;
double n;
double calc(double x){
    return x * x * x > n;
}
int main(){
    //freopen("in","r",stdin);
    ios::sync_with_stdio(0);
    cin >> n;
    double l = -10000,r = 10000;
   double eps = 1e-8;
   while(l + eps < r){
       double mid = (l + r) / 2;
       if(calc(mid)) r = mid;
       else l = mid;
   }
   cout << fixed << setprecision(6) << l;
    return 0;
}