#include<stdio.h>

#define PI 1.6449340668482426

int main(){
	double h,i,x,x2,ans=0.0;
	scanf("%lf",&x);
	i=1.0;
	x2=x*x;
	while((h=(x2+x*i*2.0)/(i*i*(i+x)*(i+x)))>0.000000000000000001){
		ans+=h;
		i+=1.0;
	}
	printf("%15.14f\n",PI-ans);
	return 0;
}