#include<algorithm>
#include<iostream>
#include<cmath>
#include<vector>
#include<iomanip>
using namespace std;
typedef long long lint;
typedef vector<int>vi;
typedef pair<int,int>pii;
#define rep(i,n)for(int i=0;i<(int)(n);++i)

#define ANS0 2.07079632677096370230
#define N 1000000

double sinc(double x){return x==0?1:sin(x)/x;}
double sincsq(double x){double a=sinc(x);return a*a;}

int main(){
  double x;cin>>x;
  double a=ANS0;
  rep(i,N){
    a+=sincsq(x+i)-sincsq(i);
  }
  cout<<setprecision(15)<<a<<endl;
}