#include<stdio.h>
#include<math.h>
main()
{
  float pi,s=1.0,q=1.0;
  int  a,b,c;
  int n=0,k=1;
  do{

     a=2*n+1;
     b=2*k;
     c=2*k+1;
     s=s*(b/a);
     q=q*(b/c);


      n++;
     k++;
  }while(fabs(s)>=1e-7);
   pi=s*q;
     printf("%.7f",pi);
     return 0;
}