#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
using namespace std;
double a=0.28318530717958623200;
double ans1;
int ans2,k;
int tt,x;
int main() 
{
	scanf("%d",&x);
	ans1=x*a;
	k=ans1;
	ans2=6*x+k;
	tt=ans2%10;
	ans1=ans1-k+tt;
	ans2=(ans2-tt)/10;
	if(ans2>=10)
		printf("%d%.20llf",ans2,ans1);
	else
		printf("%.20llf",ans1);
	return 0;
}