double CalcHalf(LL r1, LL r2, LL dx, LL dy)
{
    LL l2 = dx * dx + dy*dy;
    double l = sqrt( static_cast<double>(l2) );
    double x = static_cast<double>(r1*r1 - r2*r2 + l2) / (2.0 * l);
    double angle = 0.0;

    if (sqrt(2.0) * x < static_cast<double>(r1))
    {
        angle = acos( x / r1 );
    }
    else
    {
        double S = sqrt( static_cast<double>( (r1+r2)*(r1+r2) - l2 ) * static_cast<double>(l2 - (r1-r2)*(r1-r2)) ) / 4.0;
        double y = 2.0 * S / l;
        if (y / r1 < 0.1)
        {
            // SPECIAL CASE FOR SMALL ANGLES
            // asin(x)= x + 1/6 x^3 + 3/40 x^5 + 5/112 x^7 + 35/1152 x^9 + 63/2816 x^11 + 231/13312 x^13 + 143/10240 x^15 +...
            double c[12] = { 0, 0, 0, 1.0 / 6.0, 0.0, 3.0 / 40.0, 0.0, 5.0 / 112.0, 0.0, 35.0 / 1152.0, 0.0, 63.0 / 2816.0 };
            double v[12] = { 0 };
            double vSin = 1.0;
            double sin2A = 2.0 * (y / r1) * (x/r1);
            for (size_t i = 0; i < 12; ++i)
            {
                v[i] = vSin * c[i];
                vSin *= sin2A;
            }

            double s = 0.0;
            for (int i = 11; i >= 0; --i)
                s += v[i];

            return static_cast<double>(r1*r1) * s / 2.0;
        }

        angle = asin(y / r1);
    }

    return static_cast<double>(r1*r1) * ( 2 * angle - sin(2*angle) ) / 2.0 ;
}

void SolveD()
{
    LL x1, y1, r1;
    LL x2, y2, r2;

    cin >> x1 >> y1 >> r1;
    cin >> x2 >> y2 >> r2;

    x2 -= x1;
    y2 -= y1;
    x1 = y1 = 0;

    if ((r1 + r2)*(r1 + r2) <= x2*x2 + y2*y2)
    {
        cout << 0;
    }
    else if (x2*x2 + y2*y2 <= (r2 - r1) * (r2 - r1))
    {
        double thePi = 3.14159265358979;
        cout << std::setprecision(17) << min(r1, r2) * thePi * min(r1, r2);
    }
    else
    {
        cout << std::setprecision(17) << CalcHalf(r1, r2, x2, y2) + CalcHalf(r2, r1, x2, y2);
    }
}