#include <iostream>
#include <cmath>
#include <cassert>
#include <cstdio>

using namespace std;

#define EPS 1.0E-9
#define deq( a, b ) ( fabs((a) - (b)) < EPS )
#define dle( a, b ) ( (a) < (b) || deq(a, b) )

#define M_PI (2*acos(0.0))

class Point3D {
public:
	double x, y, z;

	void rotateonZ( double rad ) {
		double tx = x, ty = y;
		x = tx*cos(rad) - ty*sin(rad);
		y = tx*sin(rad) + ty*cos(rad);
	}

	void rotateonY( double rad ) {
		double tz = z, tx = x;
		z = tz*cos(rad) - tx*sin(rad);
		x = tz*sin(rad) + tx*cos(rad);
	}

	void rotateonX( double rad ) {
		double ty = y, tz = z;
		y = ty*cos(rad) - tz*sin(rad);
		z = ty*sin(rad) + tz*cos(rad);
	}

};

double dist( double x, double y ) {
	return sqrt(x*x + y*y);
}

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

double compute( double R, double x1, double y1, double x2, double y2 ) {
	const double d1 = dist(x1, y1);
	const double d2 = dist(x2, y2);

	const double tan1 = sqrt(d1*d1 - R*R);
	const double tan2 = sqrt(d2*d2 - R*R);
	const double theta1 = acos(R/d1);
	const double theta2 = acos(R/d2);

	double tx = R*cos(theta1);
	double ty = R*sin(theta1);

	if ( dle(tx, x2) || dle(-ty*(x2-x1)/(x1-tx), y2) )
		return dist(x1, y1, x2, y2);
	else
		return tan1 + tan2 + R*(acos(x2/d2) - (theta1 + theta2));
}

int main() {
	Point3D A, B, C;
	double R;

	cin >> A.x >> A.y >> A.z;
	cin >> B.x >> B.y >> B.z;
	cin >> C.x >> C.y >> C.z;
	cin >> R;

	A.x -= C.x, A.y -= C.y, A.z -= C.z;
	B.x -= C.x, B.y -= C.y, B.z -= C.z;
	C.x = 0.0, C.y = 0.0, C.z = 0.0;

	const double theta1 = -atan2(A.y, A.x);
	A.rotateonZ(theta1);
	B.rotateonZ(theta1);

	const double theta2 = -atan2(A.x, A.z);
	A.rotateonY(theta2 + M_PI/2);
	B.rotateonY(theta2 + M_PI/2);

	const double theta3 = -atan2(B.z, B.y);
	B.rotateonX(theta3);

	assert( deq(A.y, 0.0) && deq(A.z, 0.0) && deq(B.z, 0.0) );

	printf("%.2lf\n", compute(R, A.x, 0.0, B.x, B.y));

	return 0;
}