#include <iostream>
#include <iomanip>
#include <cmath>
#include <functional>
#include <cassert>

using namespace std;

typedef int64_t Int;
typedef long double Real;

const Real PI = std::acos(-1.0L);

Real solve(Int x1, Int y1, Int r1, Int x2, Int y2, Int r2) {
    assert(r1 >= r2);
    Int dist2 = (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);

    if (dist2 >= (r1+r2)*(r1+r2)) { // пересечений нет
        return 0;
    }
    // r1 >= dist + r2 - площадь меньшего круга
    if ((r1-r2)*(r1-r2) >= dist2) {
        return PI * r2 * r2;
    }
    Real dist = std::sqrt(Real(dist2));

    // r2^2 = r1^2 + d^2 - 2 * b * d * cos(alpha)
    // r2^2 - r1^2 - d^2 = - 2 * r1 * d * cos(alpha)
    // acos((-r2^2 + r1^2 + d^2) / r1 / d / 2)
    std::function<Real(Int, Int, Int)> angle = [](Int a, Int b, Int c) {
        // a^2 = b^2+d^2-2*b*d*cos(alpha)
        Real cos_alpha = Real(b*b+c*c-a*a) / b / c / 2;
        cos_alpha = std::min(cos_alpha,  1.0L);
        cos_alpha = std::max(cos_alpha, -1.0L);
        return std::acos(cos_alpha);
    };

    if (r1 * r1 >= dist2 + r2 * r2) { // угол тупой
        //std::cout << "two" << std::endl;
        Real alpha = angle(r1, r2, dist);
        Real beta = angle(r2, r1, dist);
        //assert(2*alpha >= PI);
        Real s_triangle = dist * r2 * std::sin(alpha) / 2;
        Real S1 = r2 * r2 * alpha;
        Real S2 = r1 * r1 * beta - 2 * s_triangle;
        //cout << "S1 = " << S1 << ", S2 = " << S2 << endl;
        return S1 + S2;
    } else {
        Real alpha = angle(r2, r1, dist);
        Real beta = angle(r1, r2, dist);
        // sin(a) = c / r1
        // c = 2 * r1 * sin(a)
        return alpha * r1 * r1 + beta * r2 * r2 - dist * r1 * std::sin(alpha);
    }
}

int main() {
    //freopen("input.txt", "rt", stdin);

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

    if (r1 < r2) {
        swap(x1, x2);
        swap(y1, y2);
        swap(r1, r2);
    }

    cout << fixed << setprecision(8) << solve(x1, y1, r1, x2, y2, r2) << endl;

    return 0;
}