import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
{
{
Scanner in
= new Scanner
(System.
in); int n, a=1, as=a, b=1;
double sum=0.0, u=2.0;
n = in.nextInt();
for(int i=1, k=2; i<=n; i++, k++)
{
a=3*b+2*a;
b=2*as+b;
u*=(2.0/k);
sum+=u*(1.0/(1+a*a+b*b));
as=a;
}
}
}
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