#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <algorithm>

using namespace std;

const double PI = acos((double) -1);
const double sqrt2 = sqrt((double)2);

double sqr(double a)
{
	return a * a;
}

bool Equal(double a, double b)
{
	return abs(a - b) < 10e-7;
}

bool Bigger(double a, double b)
{
	return !Equal(a, b) && a > b;
}

bool EqualOrBigger(double a, double b)
{
	return Equal(a, b) || Bigger(a, b);
}

double RoundSquare(double l)
{
	return PI * sqr(l);
}

int main()
{
	//freopen("Text.txt", "r", stdin);

	double a, l;

	scanf("%lf%lf", &a, &l);

	if (EqualOrBigger(a, 2 * l))
	{
		printf("%lf", RoundSquare(l));
		return 0;
	}

	double diagHalf = (sqrt2 * a) / 2;

	if (EqualOrBigger(l, diagHalf))
	{
		printf("%lf", sqr(a));
		return 0;
	}

	double k = a / 2;
	double b = sqrt(sqr(l) - sqr(k));

	double cosd = k / l;
	double d = acos(cosd);
	double e = 2 * d;

	double S1 = sqr(l) * e / 2;

	double S3 = b * k;

	double S2 = S1 - S3;

	double answer = RoundSquare(l) - 4 * S2;

	printf("%lf", answer);

	return 0;
}