Problem: Vasya lagged behind at the University and got to the battlefield. Just joking! He's simply playing some computer game. The field is a flat platform with n trenches dug on it. The trenches are segments on a plane parallel to the coordinate axes. No two trenches intersect.

There is a huge enemy laser far away from Vasya. The laser charges for a seconds, and then shoots continuously for b seconds. Then, it charges for a seconds again. Then it shoots continuously for b seconds again and so on. Vasya knows numbers a and b. He also knows that while the laser is shooting, Vasya must be in the trench, but while the laser is charging, Vasya can safely move around the field. The main thing is to have time to hide in the trench before the shot. If Vasya reaches the trench exactly at the moment when the laser starts shooting, we believe that Vasya managed to hide. Coincidentally, the length of any trench in meters numerically does not exceed b.

Initially, Vasya is at point A. He needs to get to point B. Vasya moves at speed 1 meter per second in either direction. You can get in or out of the trench at any its point. Getting in or out of the trench takes no time. It is also possible to move in the trench, without leaving it.

What is the minimum time Vasya needs to get from point A to point B, if at the initial time the laser has just started charging? If Vasya cannot get from point A to point B, print -1. If Vasya reaches point B at the moment when the laser begins to shoot, it is believed that Vasya managed to reach point B.

Input

The first line contains two space-separated integers: a and b (1 ≤ a, b ≤ 1000), — the duration of charging and the duration of shooting, in seconds.

The second line contains four space-separated integers: Ax, Ay, Bx, By ( - 104 ≤ Ax, Ay, Bx, By ≤ 104) — the coordinates of points А and B. It is guaranteed that points A and B do not belong to any trench.

The third line contains a single integer: n (1 ≤ n ≤ 1000), — the number of trenches. 

Each of the following n lines contains four space-separated integers: x1, y1, x2, y2 ( - 104 ≤ xi, yi ≤ 104) — the coordinates of ends of the corresponding trench.

All coordinates are given in meters. It is guaranteed that for any trench either x1 = x2, or y1 = y2. No two trenches intersect. The length of any trench in meters doesn't exceed b numerically.

Output

If Vasya can get from point A to point B, print the minimum time he will need for it. Otherwise, print number -1.

The answer will be considered correct if the absolute or relative error does not exceed 10 - 4

Examples

Input

2 4
0 5 6 5
3
0 0 0 4
1 1 4 1
6 0 6 4


Output

19.0000000000


Input

5 10
0 0 10 10
1
5 0 5 9


Output

-1

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const double pi = acos(-1.0);
const double inf = 1e20;
const int maxp = 1111;
int dblcmp(double d) {
  if (fabs(d) < eps) return 0;
  return d > eps ? 1 : -1;
}
inline double sqr(double x) { return x * x; }
struct point {
  double x, y;
  point() {}
  point(double _x, double _y) : x(_x), y(_y){};
  void input() { scanf("%lf%lf", &x, &y); }
  void output() { printf("%.2f %.2f\n", x, y); }
  bool operator==(point a) const {
    return dblcmp(a.x - x) == 0 && dblcmp(a.y - y) == 0;
  }
  bool operator<(point a) const {
    return dblcmp(a.x - x) == 0 ? dblcmp(y - a.y) < 0 : x < a.x;
  }
  double len() { return hypot(x, y); }
  double len2() { return x * x + y * y; }
  double distance(point p) { return hypot(x - p.x, y - p.y); }
  point add(point p) { return point(x + p.x, y + p.y); }
  point sub(point p) { return point(x - p.x, y - p.y); }
  point mul(double b) { return point(x * b, y * b); }
  point div(double b) { return point(x / b, y / b); }
  double dot(point p) { return x * p.x + y * p.y; }
  double det(point p) { return x * p.y - y * p.x; }
  double rad(point a, point b) {
    point p = *this;
    return fabs(atan2(fabs(a.sub(p).det(b.sub(p))), a.sub(p).dot(b.sub(p))));
  }
  point trunc(double r) {
    double l = len();
    if (!dblcmp(l)) return *this;
    r /= l;
    return point(x * r, y * r);
  }
  point rotleft() { return point(-y, x); }
  point rotright() { return point(y, -x); }
  point rotate(point p, double angle) {
    point v = this->sub(p);
    double c = cos(angle), s = sin(angle);
    return point(p.x + v.x * c - v.y * s, p.y + v.x * s + v.y * c);
  }
};
struct line {
  point a, b;
  line() {}
  line(point _a, point _b) {
    a = _a;
    b = _b;
  }
  bool operator==(line v) { return (a == v.a) && (b == v.b); }
  line(point p, double angle) {
    a = p;
    if (dblcmp(angle - pi / 2) == 0) {
      b = a.add(point(0, 1));
    } else {
      b = a.add(point(1, tan(angle)));
    }
  }
  line(double _a, double _b, double _c) {
    if (dblcmp(_a) == 0) {
      a = point(0, -_c / _b);
      b = point(1, -_c / _b);
    } else if (dblcmp(_b) == 0) {
      a = point(-_c / _a, 0);
      b = point(-_c / _a, 1);
    } else {
      a = point(0, -_c / _b);
      b = point(1, (-_c - _a) / _b);
    }
  }
  void input() {
    a.input();
    b.input();
  }
  void adjust() {
    if (b < a) swap(a, b);
  }
  double length() { return a.distance(b); }
  double angle() {
    double k = atan2(b.y - a.y, b.x - a.x);
    if (dblcmp(k) < 0) k += pi;
    if (dblcmp(k - pi) == 0) k -= pi;
    return k;
  }
  int relation(point p) {
    int c = dblcmp(p.sub(a).det(b.sub(a)));
    if (c < 0) return 1;
    if (c > 0) return 2;
    return 3;
  }
  bool pointonseg(point p) {
    return dblcmp(p.sub(a).det(b.sub(a))) == 0 &&
           dblcmp(p.sub(a).dot(p.sub(b))) <= 0;
  }
  bool parallel(line v) { return dblcmp(b.sub(a).det(v.b.sub(v.a))) == 0; }
  int segcrossseg(line v) {
    int d1 = dblcmp(b.sub(a).det(v.a.sub(a)));
    int d2 = dblcmp(b.sub(a).det(v.b.sub(a)));
    int d3 = dblcmp(v.b.sub(v.a).det(a.sub(v.a)));
    int d4 = dblcmp(v.b.sub(v.a).det(b.sub(v.a)));
    if ((d1 ^ d2) == -2 && (d3 ^ d4) == -2) return 2;
    return (d1 == 0 && dblcmp(v.a.sub(a).dot(v.a.sub(b))) <= 0 ||
            d2 == 0 && dblcmp(v.b.sub(a).dot(v.b.sub(b))) <= 0 ||
            d3 == 0 && dblcmp(a.sub(v.a).dot(a.sub(v.b))) <= 0 ||
            d4 == 0 && dblcmp(b.sub(v.a).dot(b.sub(v.b))) <= 0);
  }
  int linecrossseg(line v) {
    int d1 = dblcmp(b.sub(a).det(v.a.sub(a)));
    int d2 = dblcmp(b.sub(a).det(v.b.sub(a)));
    if ((d1 ^ d2) == -2) return 2;
    return (d1 == 0 || d2 == 0);
  }
  int linecrossline(line v) {
    if ((*this).parallel(v)) {
      return v.relation(a) == 3;
    }
    return 2;
  }
  point crosspoint(line v) {
    double a1 = v.b.sub(v.a).det(a.sub(v.a));
    double a2 = v.b.sub(v.a).det(b.sub(v.a));
    return point((a.x * a2 - b.x * a1) / (a2 - a1),
                 (a.y * a2 - b.y * a1) / (a2 - a1));
  }
  double dispointtoline(point p) {
    return fabs(p.sub(a).det(b.sub(a))) / length();
  }
  double dispointtoseg(point p) {
    if (dblcmp(p.sub(b).dot(a.sub(b))) < 0 ||
        dblcmp(p.sub(a).dot(b.sub(a))) < 0) {
      return min(p.distance(a), p.distance(b));
    }
    return dispointtoline(p);
  }
  point lineprog(point p) {
    return a.add(b.sub(a).mul(b.sub(a).dot(p.sub(a)) / b.sub(a).len2()));
  }
  point symmetrypoint(point p) {
    point q = lineprog(p);
    return point(2 * q.x - p.x, 2 * q.y - p.y);
  }
};
struct circle {
  point p;
  double r;
  circle() {}
  circle(point _p, double _r) : p(_p), r(_r){};
  circle(double x, double y, double _r) : p(point(x, y)), r(_r){};
  circle(point a, point b, point c) {
    p = line(a.add(b).div(2), a.add(b).div(2).add(b.sub(a).rotleft()))
            .crosspoint(
                line(c.add(b).div(2), c.add(b).div(2).add(b.sub(c).rotleft())));
    r = p.distance(a);
  }
  circle(point a, point b, point c, bool t) {
    line u, v;
    double m = atan2(b.y - a.y, b.x - a.x), n = atan2(c.y - a.y, c.x - a.x);
    u.a = a;
    u.b = u.a.add(point(cos((n + m) / 2), sin((n + m) / 2)));
    v.a = b;
    m = atan2(a.y - b.y, a.x - b.x), n = atan2(c.y - b.y, c.x - b.x);
    v.b = v.a.add(point(cos((n + m) / 2), sin((n + m) / 2)));
    p = u.crosspoint(v);
    r = line(a, b).dispointtoseg(p);
  }
  void input() {
    p.input();
    scanf("%lf", &r);
  }
  void output() { printf("%.2lf %.2lf %.2lf\n", p.x, p.y, r); }
  bool operator==(circle v) { return ((p == v.p) && dblcmp(r - v.r) == 0); }
  bool operator<(circle v) const {
    return ((p < v.p) || (p == v.p) && dblcmp(r - v.r) < 0);
  }
  double area() { return pi * sqr(r); }
  double circumference() { return 2 * pi * r; }
  int relation(point b) {
    double dst = b.distance(p);
    if (dblcmp(dst - r) < 0) return 2;
    if (dblcmp(dst - r) == 0) return 1;
    return 0;
  }
  int relationseg(line v) {
    double dst = v.dispointtoseg(p);
    if (dblcmp(dst - r) < 0) return 2;
    if (dblcmp(dst - r) == 0) return 1;
    return 0;
  }
  int relationline(line v) {
    double dst = v.dispointtoline(p);
    if (dblcmp(dst - r) < 0) return 2;
    if (dblcmp(dst - r) == 0) return 1;
    return 0;
  }
  int getcircle(point a, point b, double r, circle &c1, circle &c2) {
    circle x(a, r), y(b, r);
    int t = x.pointcrosscircle(y, c1.p, c2.p);
    if (!t) return 0;
    c1.r = c2.r = r;
    return t;
  }
  int getcircle(line u, point q, double r1, circle &c1, circle &c2) {
    double dis = u.dispointtoline(q);
    if (dblcmp(dis - r1 * 2) > 0) return 0;
    if (dblcmp(dis) == 0) {
      c1.p = q.add(u.b.sub(u.a).rotleft().trunc(r1));
      c2.p = q.add(u.b.sub(u.a).rotright().trunc(r1));
      c1.r = c2.r = r1;
      return 2;
    }
    line u1 = line(u.a.add(u.b.sub(u.a).rotleft().trunc(r1)),
                   u.b.add(u.b.sub(u.a).rotleft().trunc(r1)));
    line u2 = line(u.a.add(u.b.sub(u.a).rotright().trunc(r1)),
                   u.b.add(u.b.sub(u.a).rotright().trunc(r1)));
    circle cc = circle(q, r1);
    point p1, p2;
    if (!cc.pointcrossline(u1, p1, p2)) cc.pointcrossline(u2, p1, p2);
    c1 = circle(p1, r1);
    if (p1 == p2) {
      c2 = c1;
      return 1;
    }
    c2 = circle(p2, r1);
    return 2;
  }
  int getcircle(line u, line v, double r1, circle &c1, circle &c2, circle &c3,
                circle &c4) {
    if (u.parallel(v)) return 0;
    line u1 = line(u.a.add(u.b.sub(u.a).rotleft().trunc(r1)),
                   u.b.add(u.b.sub(u.a).rotleft().trunc(r1)));
    line u2 = line(u.a.add(u.b.sub(u.a).rotright().trunc(r1)),
                   u.b.add(u.b.sub(u.a).rotright().trunc(r1)));
    line v1 = line(v.a.add(v.b.sub(v.a).rotleft().trunc(r1)),
                   v.b.add(v.b.sub(v.a).rotleft().trunc(r1)));
    line v2 = line(v.a.add(v.b.sub(v.a).rotright().trunc(r1)),
                   v.b.add(v.b.sub(v.a).rotright().trunc(r1)));
    c1.r = c2.r = c3.r = c4.r = r1;
    c1.p = u1.crosspoint(v1);
    c2.p = u1.crosspoint(v2);
    c3.p = u2.crosspoint(v1);
    c4.p = u2.crosspoint(v2);
    return 4;
  }
  int getcircle(circle cx, circle cy, double r1, circle &c1, circle &c2) {
    circle x(cx.p, r1 + cx.r), y(cy.p, r1 + cy.r);
    int t = x.pointcrosscircle(y, c1.p, c2.p);
    if (!t) return 0;
    c1.r = c2.r = r1;
    return t;
  }
  int pointcrossline(line v, point &p1, point &p2) {
    if (!(*this).relationline(v)) return 0;
    point a = v.lineprog(p);
    double d = v.dispointtoline(p);
    d = sqrt(r * r - d * d);
    if (dblcmp(d) == 0) {
      p1 = a;
      p2 = a;
      return 1;
    }
    p1 = a.sub(v.b.sub(v.a).trunc(d));
    p2 = a.add(v.b.sub(v.a).trunc(d));
    return 2;
  }
  int relationcircle(circle v) {
    double d = p.distance(v.p);
    if (dblcmp(d - r - v.r) > 0) return 5;
    if (dblcmp(d - r - v.r) == 0) return 4;
    double l = fabs(r - v.r);
    if (dblcmp(d - r - v.r) < 0 && dblcmp(d - l) > 0) return 3;
    if (dblcmp(d - l) == 0) return 2;
    if (dblcmp(d - l) < 0) return 1;
  }
  int pointcrosscircle(circle v, point &p1, point &p2) {
    int rel = relationcircle(v);
    if (rel == 1 || rel == 5) return 0;
    double d = p.distance(v.p);
    double l = (d + (sqr(r) - sqr(v.r)) / d) / 2;
    double h = sqrt(sqr(r) - sqr(l));
    p1 = p.add(v.p.sub(p).trunc(l).add(v.p.sub(p).rotleft().trunc(h)));
    p2 = p.add(v.p.sub(p).trunc(l).add(v.p.sub(p).rotright().trunc(h)));
    if (rel == 2 || rel == 4) {
      return 1;
    }
    return 2;
  }
  int tangentline(point q, line &u, line &v) {
    int x = relation(q);
    if (x == 2) return 0;
    if (x == 1) {
      u = line(q, q.add(q.sub(p).rotleft()));
      v = u;
      return 1;
    }
    double d = p.distance(q);
    double l = sqr(r) / d;
    double h = sqrt(sqr(r) - sqr(l));
    u = line(q, p.add(q.sub(p).trunc(l).add(q.sub(p).rotleft().trunc(h))));
    v = line(q, p.add(q.sub(p).trunc(l).add(q.sub(p).rotright().trunc(h))));
    return 2;
  }
  double areacircle(circle v) {
    int rel = relationcircle(v);
    if (rel >= 4) return 0.0;
    if (rel <= 2) return min(area(), v.area());
    double d = p.distance(v.p);
    double hf = (r + v.r + d) / 2.0;
    double ss = 2 * sqrt(hf * (hf - r) * (hf - v.r) * (hf - d));
    double a1 = acos((r * r + d * d - v.r * v.r) / (2.0 * r * d));
    a1 = a1 * r * r;
    double a2 = acos((v.r * v.r + d * d - r * r) / (2.0 * v.r * d));
    a2 = a2 * v.r * v.r;
    return a1 + a2 - ss;
  }
  double areatriangle(point a, point b) {
    if (dblcmp(p.sub(a).det(p.sub(b)) == 0)) return 0.0;
    point q[5];
    int len = 0;
    q[len++] = a;
    line l(a, b);
    point p1, p2;
    if (pointcrossline(l, q[1], q[2]) == 2) {
      if (dblcmp(a.sub(q[1]).dot(b.sub(q[1]))) < 0) q[len++] = q[1];
      if (dblcmp(a.sub(q[2]).dot(b.sub(q[2]))) < 0) q[len++] = q[2];
    }
    q[len++] = b;
    if (len == 4 && (dblcmp(q[0].sub(q[1]).dot(q[2].sub(q[1]))) > 0))
      swap(q[1], q[2]);
    double res = 0;
    int i;
    for (i = 0; i < len - 1; i++) {
      if (relation(q[i]) == 0 || relation(q[i + 1]) == 0) {
        double arg = p.rad(q[i], q[i + 1]);
        res += r * r * arg / 2.0;
      } else {
        res += fabs(q[i].sub(p).det(q[i + 1].sub(p)) / 2.0);
      }
    }
    return res;
  }
};
struct polygon {
  int n;
  point p[maxp];
  line l[maxp];
  void input() {
    for (int i = 0; i < n; i++) {
      p[i].input();
    }
  }
  void add(point q) { p[n++] = q; }
  void getline() {
    for (int i = 0; i < n; i++) {
      l[i] = line(p[i], p[(i + 1) % n]);
    }
  }
  struct cmp {
    point p;
    cmp(const point &p0) { p = p0; }
    bool operator()(const point &aa, const point &bb) {
      point a = aa, b = bb;
      int d = dblcmp(a.sub(p).det(b.sub(p)));
      if (d == 0) {
        return dblcmp(a.distance(p) - b.distance(p)) < 0;
      }
      return d > 0;
    }
  };
  void norm() {
    point mi = p[0];
    for (int i = 1; i < n; i++) mi = min(mi, p[i]);
    sort(p, p + n, cmp(mi));
  }
  void getconvex(polygon &convex) {
    int i, j, k;
    sort(p, p + n);
    convex.n = n;
    for (i = 0; i < min(n, 2); i++) {
      convex.p[i] = p[i];
    }
    if (n <= 2) return;
    int &top = convex.n;
    top = 1;
    for (i = 2; i < n; i++) {
      while (top &&
             convex.p[top].sub(p[i]).det(convex.p[top - 1].sub(p[i])) <= 0)
        top--;
      convex.p[++top] = p[i];
    }
    int temp = top;
    convex.p[++top] = p[n - 2];
    for (i = n - 3; i >= 0; i--) {
      while (top != temp &&
             convex.p[top].sub(p[i]).det(convex.p[top - 1].sub(p[i])) <= 0)
        top--;
      convex.p[++top] = p[i];
    }
  }
  bool isconvex() {
    bool s[3];
    memset(s, 0, sizeof(s));
    int i, j, k;
    for (i = 0; i < n; i++) {
      j = (i + 1) % n;
      k = (j + 1) % n;
      s[dblcmp(p[j].sub(p[i]).det(p[k].sub(p[i]))) + 1] = 1;
      if (s[0] && s[2]) return 0;
    }
    return 1;
  }
  int relationpoint(point q) {
    int i, j;
    for (i = 0; i < n; i++) {
      if (p[i] == q) return 3;
    }
    getline();
    for (i = 0; i < n; i++) {
      if (l[i].pointonseg(q)) return 2;
    }
    int cnt = 0;
    for (i = 0; i < n; i++) {
      j = (i + 1) % n;
      int k = dblcmp(q.sub(p[j]).det(p[i].sub(p[j])));
      int u = dblcmp(p[i].y - q.y);
      int v = dblcmp(p[j].y - q.y);
      if (k > 0 && u < 0 && v >= 0) cnt++;
      if (k < 0 && v < 0 && u >= 0) cnt--;
    }
    return cnt != 0;
  }
  int relationline(line u) {
    int i, j, k = 0;
    getline();
    for (i = 0; i < n; i++) {
      if (l[i].segcrossseg(u) == 2) return 1;
      if (l[i].segcrossseg(u) == 1) k = 1;
    }
    if (!k) return 0;
    vector<point> vp;
    for (i = 0; i < n; i++) {
      if (l[i].segcrossseg(u)) {
        if (l[i].parallel(u)) {
          vp.push_back(u.a);
          vp.push_back(u.b);
          vp.push_back(l[i].a);
          vp.push_back(l[i].b);
          continue;
        }
        vp.push_back(l[i].crosspoint(u));
      }
    }
    sort(vp.begin(), vp.end());
    int sz = vp.size();
    for (i = 0; i < sz - 1; i++) {
      point mid = vp[i].add(vp[i + 1]).div(2);
      if (relationpoint(mid) == 1) return 1;
    }
    return 2;
  }
  void convexcut(line u, polygon &po) {
    int i, j, k;
    int &top = po.n;
    top = 0;
    for (i = 0; i < n; i++) {
      int d1 = dblcmp(p[i].sub(u.a).det(u.b.sub(u.a)));
      int d2 = dblcmp(p[(i + 1) % n].sub(u.a).det(u.b.sub(u.a)));
      if (d1 >= 0) po.p[top++] = p[i];
      if (d1 * d2 < 0) po.p[top++] = u.crosspoint(line(p[i], p[(i + 1) % n]));
    }
  }
  double getcircumference() {
    double sum = 0;
    int i;
    for (i = 0; i < n; i++) {
      sum += p[i].distance(p[(i + 1) % n]);
    }
    return sum;
  }
  double getarea() {
    double sum = 0;
    int i;
    for (i = 0; i < n; i++) {
      sum += p[i].det(p[(i + 1) % n]);
    }
    return fabs(sum) / 2;
  }
  bool getdir() {
    double sum = 0;
    int i;
    for (i = 0; i < n; i++) {
      sum += p[i].det(p[(i + 1) % n]);
    }
    if (dblcmp(sum) > 0) return 1;
    return 0;
  }
  point getbarycentre() {
    point ret(0, 0);
    double area = 0;
    int i;
    for (i = 1; i < n - 1; i++) {
      double tmp = p[i].sub(p[0]).det(p[i + 1].sub(p[0]));
      if (dblcmp(tmp) == 0) continue;
      area += tmp;
      ret.x += (p[0].x + p[i].x + p[i + 1].x) / 3 * tmp;
      ret.y += (p[0].y + p[i].y + p[i + 1].y) / 3 * tmp;
    }
    if (dblcmp(area)) ret = ret.div(area);
    return ret;
  }
  double areaintersection(polygon po) {}
  double areaunion(polygon po) {
    return getarea() + po.getarea() - areaintersection(po);
  }
  double areacircle(circle c) {
    int i, j, k, l, m;
    double ans = 0;
    for (i = 0; i < n; i++) {
      int j = (i + 1) % n;
      if (dblcmp(p[j].sub(c.p).det(p[i].sub(c.p))) >= 0) {
        ans += c.areatriangle(p[i], p[j]);
      } else {
        ans -= c.areatriangle(p[i], p[j]);
      }
    }
    return fabs(ans);
  }
  int relationcircle(circle c) {
    getline();
    int i, x = 2;
    if (relationpoint(c.p) != 1) return 0;
    for (i = 0; i < n; i++) {
      if (c.relationseg(l[i]) == 2) return 0;
      if (c.relationseg(l[i]) == 1) x = 1;
    }
    return x;
  }
  void find(int st, point tri[], circle &c) {
    if (!st) {
      c = circle(point(0, 0), -2);
    }
    if (st == 1) {
      c = circle(tri[0], 0);
    }
    if (st == 2) {
      c = circle(tri[0].add(tri[1]).div(2), tri[0].distance(tri[1]) / 2.0);
    }
    if (st == 3) {
      c = circle(tri[0], tri[1], tri[2]);
    }
  }
  void solve(int cur, int st, point tri[], circle &c) {
    find(st, tri, c);
    if (st == 3) return;
    int i;
    for (i = 0; i < cur; i++) {
      if (dblcmp(p[i].distance(c.p) - c.r) > 0) {
        tri[st] = p[i];
        solve(i, st + 1, tri, c);
      }
    }
  }
  circle mincircle() {
    random_shuffle(p, p + n);
    point tri[4];
    circle c;
    solve(n, 0, tri, c);
    return c;
  }
  int circlecover(double r) {
    int ans = 0, i, j;
    vector<pair<double, int> > v;
    for (i = 0; i < n; i++) {
      v.clear();
      for (j = 0; j < n; j++)
        if (i != j) {
          point q = p[i].sub(p[j]);
          double d = q.len();
          if (dblcmp(d - 2 * r) <= 0) {
            double arg = atan2(q.y, q.x);
            if (dblcmp(arg) < 0) arg += 2 * pi;
            double t = acos(d / (2 * r));
            v.push_back(make_pair(arg - t + 2 * pi, -1));
            v.push_back(make_pair(arg + t + 2 * pi, 1));
          }
        }
      sort(v.begin(), v.end());
      int cur = 0;
      for (j = 0; j < v.size(); j++) {
        if (v[j].second == -1)
          ++cur;
        else
          --cur;
        ans = max(ans, cur);
      }
    }
    return ans + 1;
  }
  int pointinpolygon(point q) {
    if (getdir()) reverse(p, p + n);
    if (dblcmp(q.sub(p[0]).det(p[n - 1].sub(p[0]))) == 0) {
      if (line(p[n - 1], p[0]).pointonseg(q)) return n - 1;
      return -1;
    }
    int low = 1, high = n - 2, mid;
    while (low <= high) {
      mid = (low + high) >> 1;
      if (dblcmp(q.sub(p[0]).det(p[mid].sub(p[0]))) >= 0 &&
          dblcmp(q.sub(p[0]).det(p[mid + 1].sub(p[0]))) < 0) {
        polygon c;
        c.p[0] = p[mid];
        c.p[1] = p[mid + 1];
        c.p[2] = p[0];
        c.n = 3;
        if (c.relationpoint(q)) return mid;
        return -1;
      }
      if (dblcmp(q.sub(p[0]).det(p[mid].sub(p[0]))) > 0) {
        low = mid + 1;
      } else {
        high = mid - 1;
      }
    }
    return -1;
  }
};
struct polygons {
  vector<polygon> p;
  polygons() { p.clear(); }
  void clear() { p.clear(); }
  void push(polygon q) {
    if (dblcmp(q.getarea())) p.push_back(q);
  }
  vector<pair<double, int> > e;
  void ins(point s, point t, point X, int i) {
    double r = fabs(t.x - s.x) > eps ? (X.x - s.x) / (t.x - s.x)
                                     : (X.y - s.y) / (t.y - s.y);
    r = min(r, 1.0);
    r = max(r, 0.0);
    e.push_back(make_pair(r, i));
  }
  double polyareaunion() {
    double ans = 0.0;
    int c0, c1, c2, i, j, k, w;
    for (i = 0; i < p.size(); i++) {
      if (p[i].getdir() == 0) reverse(p[i].p, p[i].p + p[i].n);
    }
    for (i = 0; i < p.size(); i++) {
      for (k = 0; k < p[i].n; k++) {
        point &s = p[i].p[k], &t = p[i].p[(k + 1) % p[i].n];
        if (!dblcmp(s.det(t))) continue;
        e.clear();
        e.push_back(make_pair(0.0, 1));
        e.push_back(make_pair(1.0, -1));
        for (j = 0; j < p.size(); j++)
          if (i != j) {
            for (w = 0; w < p[j].n; w++) {
              point a = p[j].p[w], b = p[j].p[(w + 1) % p[j].n],
                    c = p[j].p[(w - 1 + p[j].n) % p[j].n];
              c0 = dblcmp(t.sub(s).det(c.sub(s)));
              c1 = dblcmp(t.sub(s).det(a.sub(s)));
              c2 = dblcmp(t.sub(s).det(b.sub(s)));
              if (c1 * c2 < 0)
                ins(s, t, line(s, t).crosspoint(line(a, b)), -c2);
              else if (!c1 && c0 * c2 < 0)
                ins(s, t, a, -c2);
              else if (!c1 && !c2) {
                int c3 = dblcmp(t.sub(s).det(p[j].p[(w + 2) % p[j].n].sub(s)));
                int dp = dblcmp(t.sub(s).dot(b.sub(a)));
                if (dp && c0)
                  ins(s, t, a, dp > 0 ? c0 * ((j > i) ^ (c0 < 0)) : -(c0 < 0));
                if (dp && c3)
                  ins(s, t, b, dp > 0 ? -c3 * ((j > i) ^ (c3 < 0)) : c3 < 0);
              }
            }
          }
        sort(e.begin(), e.end());
        int ct = 0;
        double tot = 0.0, last;
        for (j = 0; j < e.size(); j++) {
          if (ct == 1) tot += e[j].first - last;
          ct += e[j].second;
          last = e[j].first;
        }
        ans += s.det(t) * tot;
      }
    }
    return fabs(ans) * 0.5;
  }
};
const int maxn = 500;
struct circles {
  circle c[maxn];
  double ans[maxn];
  double pre[maxn];
  int n;
  circles() {}
  void add(circle cc) { c[n++] = cc; }
  bool inner(circle x, circle y) {
    if (x.relationcircle(y) != 1) return 0;
    return dblcmp(x.r - y.r) <= 0 ? 1 : 0;
  }
  void init_or() {
    int i, j, k = 0;
    bool mark[maxn] = {0};
    for (i = 0; i < n; i++) {
      for (j = 0; j < n; j++)
        if (i != j && !mark[j]) {
          if ((c[i] == c[j]) || inner(c[i], c[j])) break;
        }
      if (j < n) mark[i] = 1;
    }
    for (i = 0; i < n; i++)
      if (!mark[i]) c[k++] = c[i];
    n = k;
  }
  void init_and() {
    int i, j, k = 0;
    bool mark[maxn] = {0};
    for (i = 0; i < n; i++) {
      for (j = 0; j < n; j++)
        if (i != j && !mark[j]) {
          if ((c[i] == c[j]) || inner(c[j], c[i])) break;
        }
      if (j < n) mark[i] = 1;
    }
    for (i = 0; i < n; i++)
      if (!mark[i]) c[k++] = c[i];
    n = k;
  }
  double areaarc(double th, double r) { return 0.5 * sqr(r) * (th - sin(th)); }
  void getarea() {
    int i, j, k;
    memset(ans, 0, sizeof(ans));
    vector<pair<double, int> > v;
    for (i = 0; i < n; i++) {
      v.clear();
      v.push_back(make_pair(-pi, 1));
      v.push_back(make_pair(pi, -1));
      for (j = 0; j < n; j++)
        if (i != j) {
          point q = c[j].p.sub(c[i].p);
          double ab = q.len(), ac = c[i].r, bc = c[j].r;
          if (dblcmp(ab + ac - bc) <= 0) {
            v.push_back(make_pair(-pi, 1));
            v.push_back(make_pair(pi, -1));
            continue;
          }
          if (dblcmp(ab + bc - ac) <= 0) continue;
          if (dblcmp(ab - ac - bc) > 0) continue;
          double th = atan2(q.y, q.x),
                 fai = acos((ac * ac + ab * ab - bc * bc) / (2.0 * ac * ab));
          double a0 = th - fai;
          if (dblcmp(a0 + pi) < 0) a0 += 2 * pi;
          double a1 = th + fai;
          if (dblcmp(a1 - pi) > 0) a1 -= 2 * pi;
          if (dblcmp(a0 - a1) > 0) {
            v.push_back(make_pair(a0, 1));
            v.push_back(make_pair(pi, -1));
            v.push_back(make_pair(-pi, 1));
            v.push_back(make_pair(a1, -1));
          } else {
            v.push_back(make_pair(a0, 1));
            v.push_back(make_pair(a1, -1));
          }
        }
      sort(v.begin(), v.end());
      int cur = 0;
      for (j = 0; j < v.size(); j++) {
        if (cur && dblcmp(v[j].first - pre[cur])) {
          ans[cur] += areaarc(v[j].first - pre[cur], c[i].r);
          ans[cur] +=
              0.5 * point(c[i].p.x + c[i].r * cos(pre[cur]),
                          c[i].p.y + c[i].r * sin(pre[cur]))
                        .det(point(c[i].p.x + c[i].r * cos(v[j].first),
                                   c[i].p.y + c[i].r * sin(v[j].first)));
        }
        cur += v[j].second;
        pre[cur] = v[j].first;
      }
    }
    for (i = 1; i <= n; i++) {
      ans[i] -= ans[i + 1];
    }
  }
};
struct halfplane : public line {
  double angle;
  halfplane() {}
  halfplane(point _a, point _b) {
    a = _a;
    b = _b;
  }
  halfplane(line v) {
    a = v.a;
    b = v.b;
  }
  void calcangle() { angle = atan2(b.y - a.y, b.x - a.x); }
  bool operator<(const halfplane &b) const { return angle < b.angle; }
};
struct halfplanes {
  int n;
  halfplane hp[maxp];
  point p[maxp];
  int que[maxp];
  int st, ed;
  void push(halfplane tmp) { hp[n++] = tmp; }
  void unique() {
    int m = 1, i;
    for (i = 1; i < n; i++) {
      if (dblcmp(hp[i].angle - hp[i - 1].angle))
        hp[m++] = hp[i];
      else if (dblcmp(
                   hp[m - 1].b.sub(hp[m - 1].a).det(hp[i].a.sub(hp[m - 1].a)) >
                   0))
        hp[m - 1] = hp[i];
    }
    n = m;
  }
  bool halfplaneinsert() {
    int i;
    for (i = 0; i < n; i++) hp[i].calcangle();
    sort(hp, hp + n);
    unique();
    que[st = 0] = 0;
    que[ed = 1] = 1;
    p[1] = hp[0].crosspoint(hp[1]);
    for (i = 2; i < n; i++) {
      while (st < ed &&
             dblcmp((hp[i].b.sub(hp[i].a).det(p[ed].sub(hp[i].a)))) < 0)
        ed--;
      while (st < ed &&
             dblcmp((hp[i].b.sub(hp[i].a).det(p[st + 1].sub(hp[i].a)))) < 0)
        st++;
      que[++ed] = i;
      if (hp[i].parallel(hp[que[ed - 1]])) return false;
      p[ed] = hp[i].crosspoint(hp[que[ed - 1]]);
    }
    while (
        st < ed &&
        dblcmp(hp[que[st]].b.sub(hp[que[st]].a).det(p[ed].sub(hp[que[st]].a))) <
            0)
      ed--;
    while (st < ed && dblcmp(hp[que[ed]]
                                 .b.sub(hp[que[ed]].a)
                                 .det(p[st + 1].sub(hp[que[ed]].a))) < 0)
      st++;
    if (st + 1 >= ed) return false;
    return true;
  }
  void getconvex(polygon &con) {
    p[st] = hp[que[st]].crosspoint(hp[que[ed]]);
    con.n = ed - st + 1;
    int j = st, i = 0;
    for (; j <= ed; i++, j++) {
      con.p[i] = p[j];
    }
  }
};
struct point3 {
  double x, y, z;
  point3() {}
  point3(double _x, double _y, double _z) : x(_x), y(_y), z(_z){};
  void input() { scanf("%lf%lf%lf", &x, &y, &z); }
  void output() { printf("%.2lf %.2lf %.2lf\n", x, y, z); }
  bool operator==(point3 a) {
    return dblcmp(a.x - x) == 0 && dblcmp(a.y - y) == 0 && dblcmp(a.z - z) == 0;
  }
  bool operator<(point3 a) const {
    return dblcmp(a.x - x) == 0
               ? dblcmp(y - a.y) == 0 ? dblcmp(z - a.z) < 0 : y < a.y
               : x < a.x;
  }
  double len() { return sqrt(len2()); }
  double len2() { return x * x + y * y + z * z; }
  double distance(point3 p) {
    return sqrt((p.x - x) * (p.x - x) + (p.y - y) * (p.y - y) +
                (p.z - z) * (p.z - z));
  }
  point3 add(point3 p) { return point3(x + p.x, y + p.y, z + p.z); }
  point3 sub(point3 p) { return point3(x - p.x, y - p.y, z - p.z); }
  point3 mul(double d) { return point3(x * d, y * d, z * d); }
  point3 div(double d) { return point3(x / d, y / d, z / d); }
  double dot(point3 p) { return x * p.x + y * p.y + z * p.z; }
  point3 det(point3 p) {
    return point3(y * p.z - p.y * z, p.x * z - x * p.z, x * p.y - p.x * y);
  }
  double rad(point3 a, point3 b) {
    point3 p = (*this);
    return acos(a.sub(p).dot(b.sub(p)) / (a.distance(p) * b.distance(p)));
  }
  point3 trunc(double r) {
    r /= len();
    return point3(x * r, y * r, z * r);
  }
  point3 rotate(point3 o, double r) {}
};
struct line3 {
  point3 a, b;
  line3() {}
  line3(point3 _a, point3 _b) {
    a = _a;
    b = _b;
  }
  bool operator==(line3 v) { return (a == v.a) && (b == v.b); }
  void input() {
    a.input();
    b.input();
  }
  double length() { return a.distance(b); }
  bool pointonseg(point3 p) {
    return dblcmp(p.sub(a).det(p.sub(b)).len()) == 0 &&
           dblcmp(a.sub(p).dot(b.sub(p))) <= 0;
  }
  double dispointtoline(point3 p) {
    return b.sub(a).det(p.sub(a)).len() / a.distance(b);
  }
  double dispointtoseg(point3 p) {
    if (dblcmp(p.sub(b).dot(a.sub(b))) < 0 ||
        dblcmp(p.sub(a).dot(b.sub(a))) < 0) {
      return min(p.distance(a), p.distance(b));
    }
    return dispointtoline(p);
  }
  point3 lineprog(point3 p) {
    return a.add(b.sub(a).trunc(b.sub(a).dot(p.sub(a)) / b.distance(a)));
  }
  point3 rotate(point3 p, double ang) {
    if (dblcmp((p.sub(a).det(p.sub(b)).len())) == 0) return p;
    point3 f1 = b.sub(a).det(p.sub(a));
    point3 f2 = b.sub(a).det(f1);
    double len = fabs(a.sub(p).det(b.sub(p)).len() / a.distance(b));
    f1 = f1.trunc(len);
    f2 = f2.trunc(len);
    point3 h = p.add(f2);
    point3 pp = h.add(f1);
    return h.add((p.sub(h)).mul(cos(ang * 1.0)))
        .add((pp.sub(h)).mul(sin(ang * 1.0)));
  }
};
struct plane {
  point3 a, b, c, o;
  plane() {}
  plane(point3 _a, point3 _b, point3 _c) {
    a = _a;
    b = _b;
    c = _c;
    o = pvec();
  }
  plane(double _a, double _b, double _c, double _d) {
    o = point3(_a, _b, _c);
    if (dblcmp(_a) != 0) {
      a = point3((-_d - _c - _b) / _a, 1, 1);
    } else if (dblcmp(_b) != 0) {
      a = point3(1, (-_d - _c - _a) / _b, 1);
    } else if (dblcmp(_c) != 0) {
      a = point3(1, 1, (-_d - _a - _b) / _c);
    }
  }
  void input() {
    a.input();
    b.input();
    c.input();
    o = pvec();
  }
  point3 pvec() { return b.sub(a).det(c.sub(a)); }
  bool pointonplane(point3 p) { return dblcmp(p.sub(a).dot(o)) == 0; }
  int pointontriangle(point3 p) {
    if (!pointonplane(p)) return 0;
    double s = a.sub(b).det(c.sub(b)).len();
    double s1 = p.sub(a).det(p.sub(b)).len();
    double s2 = p.sub(a).det(p.sub(c)).len();
    double s3 = p.sub(b).det(p.sub(c)).len();
    if (dblcmp(s - s1 - s2 - s3)) return 0;
    if (dblcmp(s1) && dblcmp(s2) && dblcmp(s3)) return 2;
    return 1;
  }
  bool relationplane(plane f) {
    if (dblcmp(o.det(f.o).len())) return 0;
    if (pointonplane(f.a)) return 2;
    return 1;
  }
  double angleplane(plane f) {
    return acos(o.dot(f.o) / (o.len() * f.o.len()));
  }
  double dispoint(point3 p) { return fabs(p.sub(a).dot(o) / o.len()); }
  point3 pttoplane(point3 p) {
    line3 u = line3(p, p.add(o));
    crossline(u, p);
    return p;
  }
  int crossline(line3 u, point3 &p) {
    double x = o.dot(u.b.sub(a));
    double y = o.dot(u.a.sub(a));
    double d = x - y;
    if (dblcmp(fabs(d)) == 0) return 0;
    p = u.a.mul(x).sub(u.b.mul(y)).div(d);
    return 1;
  }
  int crossplane(plane f, line3 &u) {
    point3 oo = o.det(f.o);
    point3 v = o.det(oo);
    double d = fabs(f.o.dot(v));
    if (dblcmp(d) == 0) return 0;
    point3 q = a.add(v.mul(f.o.dot(f.a.sub(a)) / d));
    u = line3(q, q.add(oo));
    return 1;
  }
};
double g[1111][1111];
line l[1111];
int n;
point s, t;
double d[1111];
bool v[1111];
int main() {
  int i, j, k;
  double a, b;
  scanf("%lf%lf", &a, &b);
  s.input();
  t.input();
  scanf("%d", &n);
  for (i = 0; i < n; i++) l[i].input();
  if (dblcmp(s.distance(t) - a) <= 0) {
    printf("%.10lf\n", s.distance(t));
    return 0;
  }
  for (i = 0; i < n; i++) {
    for (j = i + 1; j < n; j++) {
      g[i][j] = 1e20;
      g[i][j] = l[i].dispointtoseg(l[j].a);
      g[i][j] = min(g[i][j], l[i].dispointtoseg(l[j].b));
      g[i][j] = min(g[i][j], l[j].dispointtoseg(l[i].a));
      g[i][j] = min(g[i][j], l[j].dispointtoseg(l[i].b));
      if (dblcmp(g[i][j] - a) > 0)
        g[i][j] = 1e20;
      else
        g[i][j] = max(g[i][j], a);
      g[i][j] += b;
      g[j][i] = g[i][j];
    }
  }
  for (i = 0; i < n; i++) {
    g[n][i] = l[i].dispointtoseg(s);
    if (dblcmp(g[n][i] - a) > 0)
      g[n][i] = 1e20;
    else
      g[n][i] = max(g[n][i], a);
    g[i][n] = g[n][i];
    g[n][i] += b;
    g[n + 1][i] = l[i].dispointtoseg(t);
    if (dblcmp(g[n + 1][i] - a) > 0) g[n + 1][i] = 1e20;
    g[i][n + 1] = g[n + 1][i];
    g[n + 1][i] = max(g[n + 1][i], a);
    g[n + 1][i] += b;
  }
  g[n][n + 1] = g[n + 1][n] = 1e15;
  for (i = 0; i < 1111; i++) d[i] = 1e15;
  d[n] = 0;
  int cnt = n + 3;
  while (cnt--) {
    double mi = 1e10;
    int pos = -1;
    for (i = 0; i < n + 2; i++)
      if (!v[i] && d[i] < mi) {
        mi = d[i];
        pos = i;
      }
    if (pos == -1) break;
    v[pos] = 1;
    for (i = 0; i < n + 2; i++)
      if (!v[i] && d[i] > d[pos] + g[pos][i]) {
        d[i] = d[pos] + g[pos][i];
      }
  }
  if (d[n + 1] > 1e11) {
    puts("-1");
  } else {
    printf("%.10lf\n", d[n + 1]);
  }
  return 0;
}