#include <cstring>

#include <cmath>

#include <algorithm>

#include <cstdlib>

#include <cstdio>

using namespace std;

struct point

{

    double x,y;

    point (double x=0,double y=0):x(x),y(y){}

};

typedef point Vector;

const double eps=1e-8;

int dcmp(double x)

{

    if(fabs(x)<eps) return 0;

    return x<0?-1:1;

}

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

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

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

double det(Vector a,Vector b){return a.x*b.y-a.y*b.x;}

double dot(Vector a,Vector b){return a.x*b.x+a.y*b.y;}

double lenth(Vector a){return sqrt(dot(a,a));}

struct line

{

    point p;

    Vector v;

    double angle;

    line(){}

    line(point p,Vector v):p(p),v(v){}

    bool operator <(const line &rht)const

    {

        return angle<rht.angle;

    }

};

struct circle

{

    point c;

    double r;

    circle(){c=point(0.0,0.0);}

    circle(point c,double r):c(c),r(r){}

    point Point(double rad)

    {

        return point(c.x+cos(rad)*r,c.y+sin(rad)*r);

    }

};

int get_circle_intersection(line L,circle C,double &t1,double &t2)

{

    t1=t2=0;

    double a=L.v.x, b=L.p.x-C.c.x,c=L.v.y,d=L.p.y-C.c.y;

    double e=a*a+c*c,f=2*(a*b+c*d),g=b*b+d*d-C.r*C.r;

    double detle = f*f-4*e*g;

    if(dcmp(detle)<0) return 0;

    if(dcmp(detle)==0) {t1=t2=-f/(2*e);return 1;}

    t1=(-f-sqrt(detle)) /(2*e);

    t2=(-f+sqrt(detle)) /(2*e);

    if(dcmp(t1)<0 || dcmp(t2)<0) return 0;//按照速度的反方向才可以和圆相交

    return 2;

}

int main()

{

    double t1,t2;

    double x1,x2;

    line tmp;

    circle tmp1;

    circle tmp2;

    double Rm, R, r;

    while(~scanf("%lf %lf %lf %lf %lf %lf %lf",&Rm,&R,&r,&tmp.p.x,&tmp.p.y,&tmp.v.x,&tmp.v.y))

    {

        Rm+=r;R+=r;

        tmp1.r=Rm;

        tmp2.r=R;

        int count1=get_circle_intersection(tmp,tmp1,t1,t2);

        int count2=get_circle_intersection(tmp,tmp2,x1,x2);

        if(count2==0)printf("0.00\n");

        else

            printf("%.3lf\n",fabs(x2-x1)-fabs(t1-t2));// 因为直线式点+向量（和速度一样）所以减法就可以了

    }

    return 0;

}