#include<iostream>
#include<iomanip>
using namespace std;
class Circle
{
    public:
    float radius;
    public:
    Circle(float r):radius(r){}
    float getCircumference()
    {
        return 2*3.14159*radius;
    }
};
int main()
{
    float radius_input;
    cin>>radius_input;
    if(radius_input>=&&radius_input<=1000)
    {
        Circle circles(radius_input);
        float circumference=Circle.getCircumference();
        cout<<fixed<<setprecision(2);
        cout<<Circumferenece<<endl;
    }
    else
    {
        cout<<"Invalid output"
    }
    return 0;
}