#include<bits/stdc++.h>
#define MAX 5000
#define inf 1<<29
#define linf 1e16
#define eps (1e-6)
#define mod 1000000007
#define pi acos(-1)
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(a) (a).begin(),(a).end()
#define pd(a) printf("%.10f\n",(double)(a))
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(a)-1;(b)<=i;i--)
#define equals(a,b) (fabs((a)-(b))<eps)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<int,double> pid;
typedef pair<double,int> pdi;
typedef vector<int> vi;
typedef vector<pii> vpi;

class Point{
public:
  double x,y;
  Point(double x=0,double y=0):x(x),y(y){}

  Point operator+(Point p){ return Point(x+p.x,y+p.y);}
  Point operator-(Point p){ return Point(x-p.x,y-p.y);}
  Point operator*(double k){ return Point(x*k,y*k);}
  Point operator/(double k){ return Point(x/k,y/k);}
  bool operator<(Point p)const{ return (x!=p.x ? x<p.x : y<p.y);}
  bool operator==(Point p)const{ return fabs(x-p.x)<eps && fabs(y-p.y)<eps;}

  double abs(){ return sqrt(norm());}
  double norm(){ return (x*x+y*y);}
};
typedef Point Vector;
typedef vector<Point> Polygon;

class Segment{
public:
  Point p1,p2;
  Segment(Point p1=Point(),Point p2=Point()):p1(p1),p2(p2){}
};
typedef Segment Line;

class Circle{
public:
  Point c;
  double r;
  Circle(Point c=Point(),double r=0.0):c(c),r(r){}
};

double norm(Vector a){ return (a.x*a.x+a.y*a.y);}
double abs(Vector a){ return sqrt(norm(a));}
double dot(Vector a,Vector b){ return (a.x*b.x+a.y*b.y);}
double cross(Vector a,Vector b){ return (a.x*b.y-a.y*b.x);}
double arg(Vector p){ 
  double res=atan2(p.y,p.x);
  if(res<0.0)res+=2*pi;
  return res;
}

Point project(Segment s,Point p){
  Vector base=(s.p2-s.p1);
  double r=(dot(p-s.p1,base)/base.norm());
  return (s.p1+base*r);
}

double getDistanceLP(Line l,Point p){
  return abs(cross(l.p2-l.p1,p-l.p1)/abs(l.p2-l.p1));
}

double getDistanceSP(Segment s,Point p){
  if(dot(s.p2-s.p1,p-s.p1)<0.0)return abs(p-s.p1);
  if(dot(s.p1-s.p2,p-s.p2)<0.0)return abs(p-s.p2);
  return getDistanceLP(s,p);
}

bool intersect(Circle c,Segment s){
  if(getDistanceSP(s,c.c)-c.r<-eps)return true;
  return false;
}

bool intersect(Line L,Segment s){
  return cross(L.p2-L.p1,s.p1-L.p1)*cross(L.p2-L.p1,s.p2-L.p1)<eps;
}

bool on(Circle c,Point p){ return equals(abs(c.c-p),c.r); }

int ccw(Point p0,Point p1,Point p2){
  Vector a=p1-p0;
  Vector b=p2-p0;
  if(cross(a,b)>eps)return 1;
  if(cross(a,b)<-eps)return -1;
  if(dot(a,b)<-eps)return 2;
  if(a.norm()<b.norm())return -2;
  return 0;
}

pair<Point,Point> getCrossPoints(Circle c,Line l){
  Vector pr=project(l,c.c);
  Vector e=(l.p2-l.p1)/abs(l.p2-l.p1);
  double base=sqrt(c.r*c.r-norm(pr-c.c));
  return mp(pr+e*base,pr-e*base);
}

Point getCrossPointLL(Line a,Line b){
  double A=cross(a.p2-a.p1,b.p2-b.p1);
  double B=cross(a.p2-a.p1,a.p2-b.p1);
  if(abs(A)<eps || abs(B)<eps)return b.p1;
  return b.p1+(b.p2-b.p1)*(B/A);
}

Point rotate(Point base,Point a,double r){
  Point b=a-base;
  a.x=b.x*cos((r/180)*M_PI)-b.y*sin((r/180)*M_PI);
  a.y=b.x*sin((r/180)*M_PI)+b.y*cos((r/180)*M_PI);
  a=a+base;
  return a;
}

pair<Point,Point> getTangent(Circle c,Point p){
  Vector v=p-c.c;
  double r=acos(c.r/abs(v))*360/(2*pi);
  v=v*c.r/abs(v);
  Point p1=rotate(c.c,c.c+v,r);
  Point p2=rotate(c.c,c.c+v,360-r);
  return mp(p1,p2);
}

int intersect(Circle a,Circle b){
  double dis=abs(a.c-b.c),sumr=a.r+b.r,minr=min(a.r,b.r),maxr=max(a.r,b.r);
  if((sumr-dis)<-eps)return 4;
  if(equals(sumr,dis))return 3;
  if((maxr-(dis+minr))<-eps)return 2;
  if(equals(dis+minr,maxr))return 1;
  return 0;
}

vector<Line> getCommonTangent(Circle a,Circle b){
  vector<Line> vp;
  int intersection=intersect(a,b);
  if(intersection==0)return vp;
  if(intersection==1){
    Vector v=b.c-a.c;
    if(b.r<a.r)v=(v*a.r)/abs(v);
    else v=(v*a.r*(-1))/abs(v);
    vp.push_back(Line(a.c+v,a.c+v));
    return vp;
  }
  if(intersection==3){
    Vector v=b.c-a.c;
    v=v*a.r/abs(v);
    vp.push_back(Line(a.c+v,a.c+v));
  }
  double d=abs(b.c-a.c),c,s;
  Vector v=(b.c-a.c)/d,v1=v*a.r,v2=v*b.r;
  Point p1,p2;

  c=sqrt(d*d-(a.r-b.r)*(a.r-b.r));
  s=(180*asin(c/d))/pi;

  if(a.r<b.r){
    vp.push_back(Line(rotate(a.c,a.c+v1,180-s),rotate(b.c,b.c-v2,360-s)));
    vp.push_back(Line(rotate(a.c,a.c+v1,180+s),rotate(b.c,b.c-v2,s)));
  }
  else {
    vp.push_back(Line(rotate(a.c,a.c+v1,s),rotate(b.c,b.c-v2,180+s)));
    vp.push_back(Line(rotate(a.c,a.c+v1,360-s),rotate(b.c,b.c-v2,180-s)));
  }
  if(intersection==2 || intersection==3)return vp;
  
  c=sqrt(d*d-(a.r+b.r)*(a.r+b.r));
  s=(180*asin(c/d))/pi;
  
  vp.push_back(Line(rotate(a.c,a.c+v1,s),rotate(b.c,b.c-v2,s)));
  vp.push_back(Line(rotate(a.c,a.c+v1,360-s),rotate(b.c,b.c-v2,360-s)));
  
  return vp;
}

double getAngle(Vector a,Vector b){
  double tmp=dot(a,b)/(abs(a)*abs(b));
  if(tmp<-1.0)tmp=-1.0;
  if(1.0<tmp)tmp=1.0;
  double r=acos(tmp)*180.0/pi;
  return r;
}

int n,r,R;
Point s,g;
vector<Point> vp;
vector<pid> e[MAX];
vector<Circle> vc;
Circle small,big,big2;
Line L(Point(0,0),Point(0,1));

void init(){
  vp.clear();
  vc.clear();
  FOR(i,0,MAX)e[i].clear();
}

void add_edge(int from,int to,double cost){
  e[from].pb(mp(to,cost));
  e[to].pb(mp(from,cost));
}

double dijkstra(){
  double d[MAX];
  priority_queue<pdi,vector<pdi>,greater<pdi> > pq;
  fill(d,d+MAX,inf);
  d[0]=0;
  pq.push(mp(0,0));

  while(pq.size()){
    pdi u=pq.top();
    pq.pop();

    if(d[u.s]-u.f<-eps)continue;
    if(u.s==1)return d[u.s];

    FOR(i,0,e[u.s].size()){
      int next=e[u.s][i].f;
      double cost=d[u.s]+e[u.s][i].s;
      if(cost-d[next]<-eps){
        d[next]=cost;
        pq.push(mp(cost,next));
      }
    }
  }
  return -1;
}

bool in(double targ){
  if(arg(vc[0].c)-targ<-eps && targ-arg(vc[1].c)<-eps)return false;
  if(arg(vc[2].c)-targ<-eps && targ-arg(vc[3].c)<-eps)return false;
  return true;
}

bool check(Segment s){
  if(intersect(L,s)){
    Point m=getCrossPointLL(L,s);
    if(R-r<abs(m))return false;
  }
  if(on(small,s.p1) && on(small,s.p2))return true;
  if(on(big,s.p1) && on(big,s.p2))return true;
  FOR(i,0,vc.size()){
    if(on(vc[i],s.p1) && on(vc[i],s.p2))return true;
    if(intersect(vc[i],s))return false;
    if(on(vc[i],s.p1) && !in(arg(s.p1)))return false;
    if(on(vc[i],s.p2) && !in(arg(s.p2)))return false;
  }
  if(intersect(small,s))return false;
  if(intersect(big,s)){
    pair<Point,Point> pp=getCrossPoints(big,s);
    if(ccw(s.p1,s.p2,pp.f)==0 && !in(arg(pp.f)))return false;
    if(ccw(s.p1,s.p2,pp.s)==0 && !in(arg(pp.s)))return false;
  }
  if(intersect(big2,s)){
    pair<Point,Point> pp=getCrossPoints(big2,s);
    if(ccw(s.p1,s.p2,pp.f)==0 && !in(arg(pp.f)))return false;
    if(ccw(s.p1,s.p2,pp.s)==0 && !in(arg(pp.s)))return false;
  }
  return true;
}

double getdis(Segment s){
  FOR(i,0,vc.size()){
    if(on(vc[i],s.p1) && on(vc[i],s.p2)){
      double ang=getAngle(vc[i].c-s.p1,vc[i].c-s.p2);
      return 2*pi*vc[i].r*ang/360.0;
    }
  }
  if(on(small,s.p1) && on(small,s.p2)){
    double ang=getAngle(small.c-s.p1,small.c-s.p2);
    return 2*pi*small.r*ang/360.0;
  }
  if(on(big,s.p1) && on(big,s.p2)){
    if(ccw(L.p2,L.p1,s.p1)*ccw(L.p2,L.p1,s.p2)<=0)return inf;
    double ang=getAngle(big.c-s.p1,big.c-s.p2);
    return 2*pi*big.r*ang/360.0;
  }
  
  return abs(s.p1-s.p2);
}

bool comp(Circle a,Circle b){
  return arg(a.c)<arg(b.c);
}

double solve(){
  double r1 = r/sin(pi/(2*n));
  if(R<r1+r)return -1;
  double y=R*sin(pi/(2*n)),x=sqrt(R*R-y*y);
  small=Circle(Point(0,0),r1);
  big=Circle(Point(0,0),r+R);
  big2=Circle(Point(0,0),R-r);

  vc.pb(Circle(Point(x,y),r));
  vc.pb(Circle(Point(-x,y),r));
  vc.pb(Circle(Point(x,-y),r));
  vc.pb(Circle(Point(-x,-y),r));
  sort(all(vc),comp);
  vc.pb(small);
  vc.pb(big);
  vp.pb(s);
  vp.pb(g);

  FOR(i,0,vc.size()){
    FOR(j,i+1,vc.size()){
      vector<Line> vl=getCommonTangent(vc[i],vc[j]);
      FOR(k,0,vl.size()){
        vp.pb(vl[k].p1);
        vp.pb(vl[k].p2);
      }
    }
  }

  FOR(i,0,vc.size()){
    pair<Point,Point> pp = getTangent(vc[i],s);
    vp.pb(pp.f);vp.pb(pp.s);
    pp = getTangent(vc[i],g);
    vp.pb(pp.f);vp.pb(pp.s);
  }

  vc.pop_back();vc.pop_back();

  FOR(i,0,vp.size()){
    FOR(j,i+1,vp.size()){
      Segment s(vp[i],vp[j]);
      if(check(s))add_edge(i,j,getdis(s));
    }
  }
  return dijkstra();
}

int main()
{
  while(cin>>n && n){
    init();
    cin>>r>>R;
    cin>>s.x>>s.y>>g.x>>g.y;
    pd(solve());
  }
  return 0;
}

Measured memory_bytes: 3908