#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");elseprintf("%.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;
}