#include <iostream>
#include <iomanip>
#include <math.h>
using namespace std;
double bin_s(double a){
double l=0, r=1000 , eps=1e-7;
while(abs(l-r)>eps){
double m=(l+r)/2;
double x=pow(m,2)+sqrt(m);
if(a>x)l=m;
else r=m;
}
return l;
}
int main() {
double a;
cin>>a;
cout<<fixed<<setprecision(8)<<bin_s(a);
return 0;
}
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