1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #include<algorithm>
 6 #define eps 1e-8    /* >0:>eps--- <0:<-eps */
 7 #define zero(x)(((x)>0?(x):-(x))<eps)
 8 #define PI acos(-1.0)
 9 #define LL long long
10 #define maxn 100100
11 #define IN freopen("in.txt","r",stdin);
12 using namespace std;
13 
14 int sign(double x)
15 {
16     if(fabs(x)<eps) return 0;
17     return x<0? -1:1;
18 }
19 
20 double Rm,R,r,x,y,vx,vy;
21 double v;
22 
23 int main(int argc, char const *argv[])
24 {
25     //IN;
26 
27     while(scanf("%lf%lf%lf%lf%lf%lf%lf",&Rm,&R,&r,&x,&y,&vx,&vy)!=EOF)
28     {
29         double a,b,c,del;
30         a = vx*vx+vy*vy;
31         b = 2.0*x*vx + 2.0*y*vy;
32         c = x*x + y*y - (R+r)*(R+r);
33 
34         del = (b*b - 4.0*a*c);
35         if(sign(del)<=0) {printf("0\n");continue;}
36 
37         del=sqrt(del);
38         double t1,t2;
39         t1 = (-b+del)/(2.0*a);t2 = (-b-del)/(2.0*a);
40         if(t1>t2) swap(t1,t2);
41         if(t1<0) {printf("0\n");continue;}
42 
43         a = vx*vx+vy*vy;
44         b = 2.0*x*vx + 2.0*y*vy;
45         c = x*x + y*y - (Rm+r)*(Rm+r);
46 
47         del = (b*b - 4.0*a*c);
48         if(sign(del)<=0) {printf("%.3lf\n",fabs(t1-t2));continue;}
49 
50         del=sqrt(del);
51         double t3,t4;
52         t3 = (-b+del)/(2.0*a);t4 = (-b-del)/(2.0*a);
53         if(t3>t4) swap(t3,t4);
54         if(t3<0) {printf("%.3lf\n",fabs(t1-t2));continue;}
55 
56         printf("%.3lf\n",2.0*fabs(t3-t1));
57     }
58 
59     return 0;
60 }