/*
ID: espr1t
LANG: C++
TASK: Ifrit Bomber 2
KEYWORDS: Geometry, Circle intersection
*/

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <string>
#include <queue>
#include <map>
#include <set>

#define MAX 1024
#define EPS 0.000000001
#define PI 3.1415926535897

using namespace std;
FILE *in; FILE *out;

double fdist(double x1, double y1, double x2, double y2)
{
	return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

double calcHeight(double r, double d)
{
	return sqrt(r * r - d * d);
}

double eval(double r1, double r2, double d)
{
	double ans = 0.0;
	ans += PI * r1 * r1;
	ans += PI * r2 * r2;
	if (r1 + r2 < d + EPS) return ans;
	if (r1 + EPS > d + r2) return PI * r1 * r1;
	if (r2 + EPS > d + r1) return PI * r2 * r2;
	
	if (r1 < r2) swap(r1, r2);
	double left = max(0.0, d - r2), right = r1;
	for (int iter = 0; iter < 200; iter++)
	{
		double mid = (left + right) / 2.0;
		
		double h1 = calcHeight(r1, mid);
		double h2 = calcHeight(r2, fabs(d - mid));
		
		if (h1 > h2) left = mid;
		else right = mid;
	}
	double height = calcHeight(r1, left);
	double angle1 = asin(height / r1);
	double angle2 = asin(height / r2);
	
	if (left < d + EPS)
	{
		ans -= angle1 * r1 * r1;
		ans += height * left;
		ans -= angle2 * r2 * r2;
		ans += height * fabs(d - left);
	}
	else
	{
		ans -= PI * r2 * r2;
		ans -= angle1 * r1 * r1;
		ans += height * left;
		ans += angle2 * r2 * r2;
		ans -= height * fabs(d - left);
	}
	return ans;
}

double inter(double r1, double r2, double d)
{
	return PI * r1 * r1 + PI * r2 * r2 - eval(r1, r2, d);
}

int main(void)
{
	in = stdin; out = stdout;
	in = fopen("circles.in", "rt"); out = fopen("circles.out", "wt");
	
	double ans = 0;
	double d, r1, r2, R1, R2;

	double x1, y1, x2, y2;
	fscanf(in, "%lf %lf %lf %lf", &x1, &y1, &r1, &R1);
	fscanf(in, "%lf %lf %lf %lf", &x2, &y2, &r2, &R2);
	d = fdist(x1, y1, x2, y2);

	ans += eval(R1, R2, d);
	ans -= eval(r1, r2, d);
	ans += inter(R1, r2, d);
	ans -= inter(r1, r2, d);
	ans += inter(r1, R2, d);
	ans -= inter(r1, r2, d);
	
	fprintf(out, "%.6lf\n", ans);
	
	return 0;
}