// 
// pi
//
#include <stdio.h>
#include <math.h>

const int n=1000000;

inline double f(double x)
{
	return 4/(x*x+1);
}

int main()
{
	double a=0.0, b=1.0;
	double h=(b-a)/n;
	double mypi=0.0;
	int i;
	
	mypi = f(a) + f(b);
	for(i=1; i<=n; i++)
	{
		mypi = mypi + f(a+i*h);
	}
	mypi = h*mypi;
	
	printf("mypi=%.10f, err=%.2e\n", mypi, fabs(mypi-4*atan(1)));

	return 0;
}