#include <iostream>
using namespace std;
double EPS=0.001;//控制精度
int main()
{
    double a;
    cin>>a;
    if(a>=0){
        double x=a/2,lastX=x+1+EPS;//至少迭代一次
        while(x-lastX>EPS||lastX-x>EPS){
            lastX=x;
            x=(x+a/x)/2;
        }
        cout<<x;
    }
    else
        cout<<"It can't be nagitive.";
    return 0;
}