#include <iostream>
#include <stdio.h>
#include <fstream.h>
#include <math.h>
#define PI 3.14159265

using namespace std;

double X1,Y1, X2, Y2;
double R1,r1, R2, r2;
double area = 0;

double circleArea(double r){
    return PI * r * r;
}

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

double max(double a, double b){
    if(a > b) return a;
    else return b;
}


double getLenseArea(double d, double rad1, double rad2){
    if(d >= rad1 + rad2) return 0;
    double h1 = (d*d + rad1*rad1 - rad2*rad2) / (2*d*rad1);
    double h2 = (d*d - rad1*rad1 + rad2*rad2) / (2*d*rad2);
    double area = rad1*rad1 * acos(h1) + rad2*rad2*acos(h2);
    double b = (-d+rad1+rad2)*(d+rad1-rad2)*(d-rad1+rad2)*(d+rad1+rad2);
    area -= 0.5*sqrt(b);
    return area;
}

int main(){
    ifstream input;
    FILE * output;
    input.open("circles.in", ios::in);

    input >> X1 >> Y1 >> r1 >> R1;
    input >> X2 >> Y2 >> r2 >> R2;

    area += circleArea(R1);
    area += circleArea(R2);
    area -= circleArea(r1);
    area -= circleArea(r2);

    double D = getDistance(X1,X2,Y1,Y2);
    area -= getLenseArea(D,R1,R2);
    area -= getLenseArea(D,r1,r2);

    area += getLenseArea(D,r1,R2);
    area += getLenseArea(D,r1,R2);

    output = fopen("circles.out", "w");
    fprintf(output, "%f", area);
    return 0;
}