/* package whatever; // don't place package name! */
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
public static void main (String[] args) throws java.lang.Exception
{
double a,x,q,s,e;
x=0.2;
e=0.000001;
a=x;
s=a;
for (int n = 0;; n++)
{
q = (-1 * x*x*(2 * n + 1)) / (2 * n*n + 5 * n + 3);
a *= q;
s += a;
if (a < e) break;
}
System.out.print(s*2/Math.sqrt(Math.PI));
}
}

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