include <cmath>

include <iomanip>

include <iostream>

using namespace std;

struct t { double x, y; t() { x = 0; y = 0; } t(double x, double y) { this->x = x; this->y = y; } t operator+(t &tt) { return t(this->x + tt.x, this->y + tt.y); }

t operator-(t &tt) { return t(this->x - tt.x, this->y - tt.y); }

bool operator==(t &p) { return ((x == p.x) && (y == p.y)); }

bool operator!=(t &p) { return !(*this == p); }

bool t_is_line_segment(t &t1, t &t2) {
    t t3 = *this;
    t a = t2 - t1;
    t b = t3 - t1;
    double sa = a.x * b.y - b.x * a.y;
    if (sa > 0.0) return false;
    if (sa < 0.0) return false;
    if ((a.x * b.x < 0.0) || (a.y * b.y < 0.0)) return false;
    if (a.length() < b.length()) return false;
    if (t1 == t3) return false;
    if (t2 == t3) return false;
    return true;
}
double distance(const t &p) {
    double a = this->x - p.x;
    double b = this->y - p.y;
    return sqrt(a * a + b * b);
}

double length(void) { return sqrt(x * x + y * y); }

};

struct line { double a, b, c; line(const t &t1, const t &t2) { a = t1.y - t2.y; b = t2.x - t1.x; c = t1.x * t2.y - t2.x * t1.y; } };

bool intersect(const line &l1, const line &l2, t &res) { if (l1.a * l2.b == l2.a * l1.b) return false; double g = l1.a * l2.b - l2.a * l1.b; res.x = -(l1.c * l2.b - l2.c * l1.b) / g; res.y = -(l1.a * l2.c - l2.a * l1.c) / g; return true; }

int main() {

t x0, x1, x2, x3, m; // m точка пересечения

double h = 6, answer = 0;

cin >> x0.x >> x0.y >> x1.x >> x1.y >> x2.x >> x2.y >> x3.x >> x3.y >> h;
double x0x1_d = x0.distance(x1);
if (((x3.y - x2.y) * (x0.x - x1.x) - (x3.x - x2.x) * (x0.y - x1.y)) == 0) {
    if (x0.t_is_line_segment(x2, x3)) {
        if (x1.t_is_line_segment(x2, x3)) {
            if (x0x1_d <= h) {
                answer = M_PI * x0x1_d/2;
            } else {
                answer = x0x1_d * asin(h / x0x1_d);
            }
        } else {
            if (x2.t_is_line_segment(x1, x3)) { 
                                        if (x0x1_d <= h) answer = x0x1_d * asin(x0.distance(x2) / x0x1_d);
                                        else if (x0x1_d * x0x1_d <= h * h + x0.distance(x2) * x0.distance(x2)){
                                                    answer = x0x1_d * (asin (h / x0x1_d) - acos(x0.distance(x2) / x0x1_d));
                                        }
                            } else {
                                        if (x0x1_d <= h) answer = x0x1_d * asin(x0.distance(x3) / x0x1_d);
                                        else if (x0x1_d * x0x1_d <= h * h + x0.distance(x3) * x0.distance(x3)){
                                                    answer = x0x1_d * (asin (h / x0x1_d) - acos(x0.distance(x3) / x0x1_d));
                                        }
            }
        }
    } else {
        double a;
        if (x1.t_is_line_segment(x2, x3)) {
            a = min(x0.distance(x2), x0.distance(x3));
            if (x0x1_d < sqrt(a * a + h * h)) {
                answer = x0x1_d * acos(a / x0x1_d);
            } else {
                answer = x0x1_d * asin(a / x0x1_d);
            }
        } else {
            a = max(x0.distance(x2), x0.distance(x3));
            if (x0x1_d < sqrt(a * a + h * h)) {
                answer = x0x1_d * (asin(h / x0x1_d) - acos(a / x0x1_d));
            }
        }
    }
} else {
    line l10(x0, x1), l23(x2, x3);
    if (intersect(l10, l23, m)) {
        if (m.t_is_line_segment(x2, x3)) {
            double x0m_d = m.distance(x0);
            answer = sqrt(x0x1_d * x0x1_d - x0m_d * x0m_d);
            if (answer > h) answer = h;
        }
    }
}
cout << fixed << setprecision(3) << answer << endl;
return 0;

}