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

using namespace std;

#define pb push_back
#define mp make_pair
#define sz(A) (int)(A).size()

typedef long long LL;
typedef long double LD;

struct vect {
    double x, y;

    vect() {}

    vect(double a, double b) {
        x = a, y = b;
    }

    void read() {
        cin >> x >> y;
    }

    double sqr_len() {
        return x * x + y * y;
    }

    void norm() {
        double l = sqrt(sqr_len());
        x /= l;
        y /= l;
    }
};

vect operator - (vect a, vect b) {
    return vect(a.x - b.x, a.y - b.y);
}

vect operator + (vect a, vect b) {
    return vect(a.x + b.x, a.y + b.y);
}

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

double operator * (vect a, vect b) {
    return a.x * b.y - a.y * b.x;
}

double eval(vect c, double r, vect v1, vect v2, double d) {
    cerr << r << " ! " << d << endl;
    cerr << (sqr(r) * 2 - sqr(d)) / (2 * sqr(r)) << endl;
    double ang = acos( (sqr(r) * 2 - sqr(d)) / (2 * sqr(r)) );
    double res = (ang / 2) * sqr(r);
    res -= abs((v1 - c) * (v2 - c)) / 2;
    return res;
}

int main() {
    freopen("area.in", "r", stdin);
    freopen("area.out", "w", stdout);

    double r1, r2;
    vect c1, c2;

    c1.read();
    cin >> r1;
    c2.read();
    cin >> r2;

    c2 = c2 - c1;
    c1 = vect(0, 0);

    cout.precision(2);
    if (c2.sqr_len() >= sqr(r1 + r2)) {
        cout << fixed << 0 << endl;
        return 0;
    }

    if (c2.sqr_len() <= sqr(r1 - r2)) {
        r1 = min(r1, r2);
        cout << fixed << M_PI * r1 * r1 << endl;
        return 0;
    }

    vect copy2 = c2;
    copy2.norm();
    double dist = (sqr(r1) + c2.sqr_len() - sqr(r2)) / (2 * sqrt(c2.sqr_len()));
    copy2.x *= dist, copy2.y *= dist;

    vect v = vect(c1.y - c2.y, c2.x - c1.x);
    v.norm();
    cerr << v.x << " " << v.y << endl;

    double A = c1.x - c2.x, B = c1.y - c2.y;
    vect mid = copy2;
    double C = - A * mid.x - B * mid.y;
    cerr << dist << endl;
    cerr << A << " " << B << " " << C << endl;
    double h = abs(C) / sqrt(A * A + B * B);
    cerr << h << endl;
    double dx = sqrt( sqr(r1) - sqr(h) );

    v.x *= dx, v.y *= dx;

    vect v1 = mid - v;
    vect v2 = mid + v;

    double res = eval(c1, r1, v1, v2, 2 * dx) + eval(c2, r2, v1, v2, 2 * dx);
    cout << fixed << res << endl;

    return 0;
}