#include <math.h>
double fun(double eps)
{
double s=1.0;float t=1,pi=0,n=1.0;
while((fabs(s))>=eps)
{
pi+=s;
t=n/(2*n+1);
s*=t;n++;
}
pi=pi*2;
return pi;
}
main()
{ double x;
printf("Input eps:");
scanf("%lf",&x); printf("\neps=%lf, PI=%lf\n",x,fun(x));
}