#include <bits/stdc++.h>

using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
constexpr ll TEN(int n) { return (n==0) ? 1 : 10*TEN(n-1); }
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;

using D = double;
const D PI = acos(D(-1)), EPS = 1e-10;

struct Pt2 {
    D x, y;
    Pt2() {}
    Pt2(D _x, D _y) : x(_x), y(_y) {}
    Pt2 operator+(const Pt2 &r) const { return Pt2(x+r.x, y+r.y); }
    Pt2 operator-(const Pt2 &r) const { return Pt2(x-r.x, y-r.y); }
    Pt2 operator*(const Pt2 &r) const { return Pt2(x*r.x-y*r.y, x*r.y+y*r.x); }

    Pt2 operator*(const D &r) const { return Pt2(x*r, y*r); }
    Pt2 operator/(const D &r) const { return Pt2(x/r, y/r); }

    Pt2& operator+=(const Pt2 &r) { return *this=*this+r; }
    Pt2& operator-=(const Pt2 &r) { return *this=*this-r; }
    Pt2& operator*=(const Pt2 &r) { return *this=*this*r; }
    Pt2& operator*=(const D &r) { return *this=*this*r; }
    Pt2& operator/=(const D &r) { return *this=*this/r; }
    
    Pt2 operator-() const { return Pt2(-x, -y); }

    D abs() const { return sqrt(x*x + y*y); }
    D rabs() const { return max(std::abs(x), std::abs(y)); } // robust abs
    D arg() const { return atan2(y, x); }

    pair<D, D> to_pair() const { return make_pair(x, y); }
    static Pt2 polar(D le, D th) { return Pt2(le*cos(th), le*sin(th)); }
};
ostream& operator<<(ostream& os, const Pt2 &p) {
    os << "(" << p.x << ", " << p.y << ")";
    return os;
}
using P = Pt2;

struct L {
    P s, t;
    L() {}
    L(P _s, P _t) : s(_s), t(_t) {}
    P vec() const { return t-s; }
    D abs() const { return vec().abs(); }
    D arg() const { return vec().arg(); }
};

int sgn(D a) {
    if (abs(a) <= EPS) return 0;
    return (a < 0) ? -1 : 1;
}
int sgn(D a, D b) { return sgn(a-b); }
//relative sign
int rsgn(D a, D f) {
    if (abs(a) <= f*EPS) return 0;
    return (a < 0) ? -1 : 1;
}
bool near(P a, P b) { return !sgn((a-b).abs()); }

//robust less
bool rless(P l, P r) {
    if (sgn(r.x-l.x)) return l.x < r.x;
    if (sgn(r.y-l.y)) return l.y < r.y;
    return false;
}

D cross(P a, P b) { return a.x*b.y - a.y*b.x; }
D dot(P a, P b) { return a.x*b.x + a.y*b.y; }

// -2, -1, 0, 1, 2 : front, clock, on, cclock, back
int ccw(P b, P c) {
    int s = rsgn(cross(b, c), b.rabs());
    if (s) return s;
    if (!sgn(c.rabs()) || !sgn((c-b).rabs())) return 0;
    if (dot(b, c) < 0) return 2;
    if (dot(-b, c-b) < 0) return -2;
    return 0;
}
int ccw(P a, P b, P c) { return ccw(b-a, c-a); }
int ccw(L l, P p) { return ccw(l.s, l.t, p); }

struct C {
    P p; D r;
    C() {}
    C(P p, D r) : p(p), r(r) {}
};

// pからcに接線を引く，交点はp1, p2
int tangent(const C &c, const P &p, P &p1, P &p2) {
    D di = (c.p - p).abs();
    int si = sgn(c.r, di);
    if (si == 1) return 0;
    D th = acos(min(D(1), c.r / di));
    D ar = (p - c.p).arg();
    p1 = c.p + P::polar(c.r, ar-th);
    p2 = c.p + P::polar(c.r, ar+th);
    if (si == 0) return 1;
    return 2;
}

//共通内接線
int internal_tangent(const C &c, const C &d, L &l, L &r) {
    D di = (c.p - d.p).abs();
    int si = sgn(c.r + d.r, di);
    if (si == 1) return 0;
    D th = acos(min(D(1), (c.r+d.r) / di));
    D ar = (d.p - c.p).arg();
    l.s = c.p + P::polar(c.r, ar-th);
    l.t = d.p - P::polar(d.r, ar-th);
    r.s = c.p + P::polar(c.r, ar+th);
    r.t = d.p - P::polar(d.r, ar+th);
    if (si == 0) return 1;
    return 2;
}

//共通外接線
int external_tangent(const C &c, const C &d, L &l, L &r) {
    D di = (c.p - d.p).abs();
    int si = sgn(abs(c.r - d.r), di);
    if (si == 1) return 0;
    assert(sgn(di)); // prohibit same circles
    D th = acos(min(D(1), max(D(-1), (c.r-d.r) / di)));
    D ar = (d.p - c.p).arg();
    l.s = c.p + P::polar(c.r, ar-th);
    l.t = d.p + P::polar(d.r, ar-th);
    r.s = c.p + P::polar(c.r, ar+th);
    r.t = d.p + P::polar(d.r, ar+th);
    if (si == 0) return 1;
    return 2;
}

int crossLL(const L &l, const L &m, P &r) {
    D cr1 = cross(l.vec(), m.vec()), cr2 = cross(l.vec(), l.t - m.s);
    if (rsgn(cr1, l.vec().rabs() + m.vec().rabs()) == 0) {
        r = l.s;
        if (rsgn(cr2, l.vec().rabs() + (l.t -m.s).rabs())) return 0;
        return 1;
    }
    r = m.s + m.vec() * (cr2 / cr1);
    return 1;
}

P project(const L &l, const P &p) {
    P v = l.vec();
    return l.s + v * (dot(v, p-l.s) / (v.x*v.x + v.y*v.y));
}
D distLP(const L &l, const P &p) {
    return abs(cross(l.vec(), p-l.s)) / l.abs();
}

//need Intersect/distLP
int crossCL(const C &c, const L &l, L &r) {
    D u = distLP(l, c.p);
    int si = sgn(u, c.r);    
    if (si == 1) return 0;
    P v = project(l, c.p);
    P di = (si == 0) ? P(0, 0) : l.vec() * (sqrt(c.r*c.r - u*u) / l.abs());
    r = L(v+di, v-di);
    if (si == 0) return 1;
    return 2;
}

bool solve() {
    int n;
    D x, y, r, R;
    P s, t;
    cin >> n >> r >> R;
    if (!n) return false;
    cin >> x >> y;
    s = P(x, y);
    cin >> x >> y;
    t = P(x, y);
    D th = PI / n;
    D z = 2 * (r / sin(th)) * cos(th / 2);
    if (z + r > R) {
        cout << "-1" << endl;
        return true;
    }
    V<C> poles(4);
    poles[0] = C(P::polar(R, th/2), r);
    poles[1] = C(P::polar(R, -th/2), r);
    poles[2] = C(P::polar(R, th/2+PI), r);
    poles[3] = C(P::polar(R, -th/2+PI), r);
    auto can = [&](P p) {
        D pd = p.abs();
        if (sgn(pd, z) == -1) return false;
        if (sgn(abs(p.x), r) == -1) {
            if (sgn(abs(p.y), R) == 1) return false;
        }
        for (auto c: poles) {
            if (sgn((c.p-p).abs(), c.r) == -1) return false;
        }
        if (sgn(pd, R-r) == 1 && sgn(pd, R+r) == -1) {
            D ar = p.arg();
            if (sgn(ar, th/2) == 1 && sgn(ar, PI-th/2) == -1) return false;
            if (sgn(ar, -th/2) == -1 && sgn(ar, -PI+th/2) == 1) return false;
        }
        return true;
    };

    V<C> circles = poles;
    circles.push_back(C(P(0, 0), R-r));
    circles.push_back(C(P(0, 0), R+r));
    circles.push_back(C(P(0, 0), z));
    V<P> pred;

    auto canl = [&](L s) {
        V<P> v = {s.s, s.t};
        for (auto c: circles) {
            L l;
            if (crossCL(c, s, l)) {
                if (ccw(s, l.s) == 0) v.push_back(l.s);
                if (ccw(s, l.t) == 0) v.push_back(l.t);
            }
        }
        P p;
        if (crossLL(s, L(P(-r, 0), P(-r, 1)), p)) {
            if (ccw(s, p) == 0) v.push_back(p);
        }
        if (crossLL(s, L(P(r, 0), P(r, 1)), p)) {
            if (ccw(s, p) == 0) v.push_back(p);
        }
        sort(begin(v), end(v), rless);
        int n = int(v.size());
        for (int i = 0; i < n-1; i++) {
            P p = (v[i]+v[i+1])/2;
            if (!can(p)) return false;
        }
        for (int i = 0; i < n; i++) assert(can(v[i]));
        return true;
    };

    for (auto c: circles) {
        P p1, p2;
        if (tangent(c, s, p1, p2)) {
            pred.push_back(p1);
            pred.push_back(p2);
        }
        if (tangent(c, t, p1, p2)) {
            pred.push_back(p1);
            pred.push_back(p2);
        }
        for (auto d: circles) {
            if (near(c.p, d.p) && sgn(c.r, d.r) == 0) continue;
            L l1, l2;
            if (internal_tangent(c, d, l1, l2)) {
                pred.insert(end(pred), {l1.s, l1.t, l2.s, l2.t});
            }
            if (external_tangent(c, d, l1, l2)) {
                pred.insert(end(pred), {l1.s, l1.t, l2.s, l2.t});
            }
        }
    }
    sort(begin(pred), end(pred), rless);
    pred.erase(unique(begin(pred), end(pred), near), end(pred));
    pred.erase(remove_if(begin(pred), end(pred), [&](P p){
        return !can(p);
    }), end(pred));
    pred.push_back(s);
    pred.push_back(t);

    int gn = int(pred.size());

    VV<D> di(gn, V<D>(gn, 1e30));
    for (int i = 0; i < gn; i++) {
        di[i][i] = 0;
        for (int j = i+1; j < gn; j++) {
            D ans = 1e100;
            P pi = pred[i], pj = pred[j];
            if (canl(L(pi, pj))) {
                ans = min(ans, (pi - pj).abs());
            }
            for (auto c: poles) {
                if (sgn((c.p - pi).abs(), c.r) == 0 && sgn((c.p - pj).abs(), c.r) == 0) {
                    D ar = fmod((pi - c.p).arg() - (pj - c.p).arg() + 4*PI, 2*PI);
                    ar = min(ar, 2*PI - ar);
                    ans = min(ans, c.r * ar);
                }
            }
            {
                C c = C(P(0, 0), z);
                if (sgn((c.p - pi).abs(), c.r) == 0 && sgn((c.p - pj).abs(), c.r) == 0) {
                    D ar = fmod((pi - c.p).arg() - (pj - c.p).arg() + 4*PI, 2*PI);
                    ar = min(ar, 2*PI - ar);
                    ans = min(ans, c.r * ar);
                }
            }
            {
                C c = C(P(0, 0), R-r);                            
                if (sgn((c.p - pi).abs(), c.r) == 0 && sgn((c.p - pj).abs(), c.r) == 0) {
                    D ar = fmod((pi - c.p).arg() - (pj - c.p).arg() + 4*PI, 2*PI);
                    ar = min(ar, 2*PI - ar);
                    ans = min(ans, c.r * ar);
                }
            }
            {
                C c = C(P(0, 0), R+r);
                if (sgn((c.p - pi).abs(), c.r) == 0 && sgn((c.p - pj).abs(), c.r) == 0
                    && sgn(pi.x) == sgn(pj.x)) {
                    assert(sgn(abs(pi.x), r) != -1);
                    assert(sgn(abs(pj.x), r) != -1);
                    D ar = fmod((pi - c.p).arg() - (pj - c.p).arg() + 4*PI, 2*PI);
                    ar = min(ar, 2*PI - ar);
                    ans = min(ans, c.r * ar);
                }
            }
            di[i][j] = di[j][i] = ans;
        }
    }

    for (int k = 0; k < gn; k++) {
        for (int i = 0; i < gn; i++) {
            for (int j = 0; j < gn; j++) {
                di[i][j] = min(di[i][j], di[i][k] + di[k][j]);
            }
        }
    }

    cout << di[gn-2][gn-1] << endl;
    return true;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << setprecision(20);

    while (solve()) {}
    return 0;
}



Measured memory_bytes: 3912