# include <stdio.h>
# define n 100000000
# define h 1/n
double f(double x)
{ double y;
  y=1/(1+x*x);
  return y;
}
void main()
{ int i;
  double f(double x);
  double s=0;
  for(i=1;i<n;i++)
  {
      s+=f(i*h);
  }
     s=(3/4+s)*h;
    printf("%lf\n",s);
}