Problem: There is a chain consisting of multiple circles on a plane. The first (last) circle of the chain only intersects with the next (previous) circle, and each intermediate circle intersects only with the two neighboring circles.

Your task is to find the shortest path that satisfies the following conditions.

* The path connects the centers of the first circle and the last circle.
* The path is confined in the chain, that is, all the points on the path are located within or on at least one of the circles.

Figure E-1 shows an example of such a chain and the corresponding shortest path.

<image>

Figure E-1: An example chain and the corresponding shortest path


Input

The input consists of multiple datasets. Each dataset represents the shape of a chain in the following format.

> n
>  x1 y1 r1
>  x2 y2 r2
>  ...
>  xn yn rn
>

The first line of a dataset contains an integer n (3 ≤ n ≤ 100) representing the number of the circles. Each of the following n lines contains three integers separated by a single space. (xi, yi) and ri represent the center position and the radius of the i-th circle Ci. You can assume that 0 ≤ xi ≤ 1000, 0 ≤ yi ≤ 1000, and 1 ≤ ri ≤ 25.

You can assume that Ci and Ci+1 (1 ≤ i ≤ n−1) intersect at two separate points. When j ≥ i+2, Ci and Cj are apart and either of them does not contain the other. In addition, you can assume that any circle does not contain the center of any other circle.

The end of the input is indicated by a line containing a zero.

Figure E-1 corresponds to the first dataset of Sample Input below. Figure E-2 shows the shortest paths for the subsequent datasets of Sample Input.

<image>

Figure E-2: Example chains and the corresponding shortest paths


Output

For each dataset, output a single line containing the length of the shortest chain-confined path between the centers of the first circle and the last circle. The value should not have an error greater than 0.001. No extra characters should appear in the output.

Sample Input


10
802 0 10
814 0 4
820 1 4
826 1 4
832 3 5
838 5 5
845 7 3
849 10 3
853 14 4
857 18 3
3
0 0 5
8 0 5
8 8 5
3
0 0 5
7 3 6
16 0 5
9
0 3 5
8 0 8
19 2 8
23 14 6
23 21 6
23 28 6
19 40 8
8 42 8
0 39 5
11
0 0 5
8 0 5
18 8 10
8 16 5
0 16 5
0 24 5
3 32 5
10 32 5
17 28 8
27 25 3
30 18 5
0


Output for the Sample Input


58.953437
11.414214
16.0
61.874812
63.195179






Example

Input

10
802 0 10
814 0 4
820 1 4
826 1 4
832 3 5
838 5 5
845 7 3
849 10 3
853 14 4
857 18 3
3
0 0 5
8 0 5
8 8 5
3
0 0 5
7 3 6
16 0 5
9
0 3 5
8 0 8
19 2 8
23 14 6
23 21 6
23 28 6
19 40 8
8 42 8
0 39 5
11
0 0 5
8 0 5
18 8 10
8 16 5
0 16 5
0 24 5
3 32 5
10 32 5
17 28 8
27 25 3
30 18 5
0


Output

58.953437
11.414214
16.0
61.874812
63.195179

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;

#define DEBUG 1

#define INF (1.0/0.0)
#define EPS 1e-8
#define PI 3.1415926535
#define EQ(x, y) (abs((x)-(y))<EPS)
#define X real()
#define Y imag()

typedef complex<double> Point;
typedef Point Vec;
typedef array<Point, 2> Line;
typedef vector<Point> Poly;

struct Circle {
  Point c;
  double r;
};

enum Geometory {ABC=-2, CW, ON_LINE, CCW, CAB, OUTSIDE, INSIDE, ERROR}; 

namespace std {
  bool operator<(Point a, Point b) {
    if (!EQ(a.X, b.X)) return a.X < b.X;
    if (!EQ(a.Y, b.Y)) return a.Y < b.Y;
    return false;
    //return a.Y < b.Y;
  }

  bool operator>(Point a, Point b) {
    return b<a;
  }

  bool operator<=(Point a, Point b) {
    return !(a>b);
  }
}

double dot(Point a, Point b) {
  return (conj(a)*b).X;
}

double cross(Point a, Point b) {
  return (conj(a)*b).Y;
}

Geometory ccw(Point a, Point b, Point c) {
  b -= a;
  c -= a;
  if (cross(b, c) > EPS) return CCW; // ccw
  if (cross(b, c) < -EPS) return CW; // cw
  if (dot(b, c) < 0) return CAB; // c - a - b
  if (norm(b) < norm(c)) return ABC; // a - b - c
  return ERROR;
}

Point proj(Line l, Point p) {
  Point v = l[1]-l[0];
  double ratio = dot(v, p-l[0]) / norm(v);
  return l[0] + ratio*v;
}

Point refl(Line l, Point p) {
  return p + (proj(l, p) - p) * 2.0;
}

Vec rotate(Vec v, double r) {
  return v*Vec(cos(r), sin(r));
}

bool IsOrthogonal(Line l, Line m) {
  Vec v1 = l[1]-l[0];
  Vec v2 = m[1]-m[0];
  return EQ(dot(v1, v2), 0.0);
}

bool IsParallel(Line l, Line m) {
  Vec v1 = l[1]-l[0];
  Vec v2 = m[1]-m[0];
  return EQ(cross(v1, v2), 0.0);
}

bool IntersectLL(Line l, Line m) {
  if (!EQ(cross(l[1]-l[0], m[1]-m[0]), 0.0)) return true;
  if (EQ(cross(l[1]-l[0], m[0]-l[0]), 0.0)) return true;
  return false;
}

bool IntersectLS(Line l, Line s) {
  Point b = l[0];
  Vec v = l[1]-l[0];
  return cross(v, s[0]-b)*cross(v, s[1]-b) < EPS;
}

bool IntersectSS(Line s, Line t) {
  if (ccw(s[0], s[1], t[0])*ccw(s[0], s[1], t[1]) > 0) return false;
  if (ccw(t[0], t[1], s[0])*ccw(t[0], t[1], s[1]) > 0) return false;
  return true;
}

bool IntersectLP(Line l, Point p) {
  return EQ(cross(l[1]-p, l[0]-p), 0.0);
}

bool IntersectSP(Line s, Point p) {
  return abs(s[0]-p)+abs(s[1]-p)-abs(s[1]-s[0]) < EPS;
}

double DistL(Line l) {
  return abs(l[0]-l[1]);
}

double DistLP(Line l, Point p) {
  return abs(p - proj(l, p));
}

double DistLL(Line l, Line m) {
  if (!IntersectLL(l, m)) return 0;
  return DistLP(l, m[0]);
}

double DistLS(Line l, Line s) {
  if (IntersectLS(l, s)) return 0;
  return min(DistLP(l, s[0]), DistLP(l, s[1]));
}

double DistSP(Line s, Point p) {
  Point r = proj(s, p);
  if (IntersectSP(s, r)) return abs(r - p);
  return min(abs(s[0]-p), abs(s[1]-p));
}

double DistSS(Line s, Line t) {
  if (IntersectSS(s, t)) return 0;

  double a = min(DistSP(s, t[0]), DistSP(s, t[1]));
  double b = min(DistSP(t, s[0]), DistSP(t, s[1]));
  return min(a, b);
}

Line PerpendBisect(Line seg) {
  Point mid = (seg[0]+seg[1])/2.0;
  return Line{mid, mid+(seg[1]-seg[0])*Vec(0, 1)};
}

Point CrossPointLL(Line l, Line m) {
  double A = cross(l[1]-l[0], m[1]-m[0]);
  double B = cross(l[1]-l[0], l[1]-m[0]);
  if (abs(A) < EPS && abs(B) < EPS) return m[0];
  if (abs(A) < EPS) assert(0);
  return m[0] + B / A * (m[1]-m[0]);
}

vector<Point> CrossPointCL(Circle c, Line l) {
  vector<Point> ret;
  double d = DistLP(l, c.c);
  if (d < c.r + EPS) {
    double ratio = (d > c.r) ? 0.0 : sqrt(c.r*c.r - d*d);
    Vec sgn = (l[0]-l[1]) / abs(l[0]-l[1]);
    ret.emplace_back(proj(l, c.c) + ratio*sgn);
    ret.emplace_back(proj(l, c.c) - ratio*sgn);
  }
  return ret;
}

vector<Point> CrossPointCS(Circle c, Line s) {
  vector<Point> ret;
  vector<Point> res = CrossPointCL(c, s);
  if (s[0] > s[1]) swap(s[0], s[1]);
  for (Point p : res) {
    if (s[0] <= p && p <= s[1]) ret.emplace_back(p);
  }
  return ret;
}

vector<Point> CrossPointCC(Circle c1, Circle c2) {
  vector<Point> ret;
  double d = abs(c1.c - c2.c);
  double rc = (d*d + c1.r*c1.r - c2.r*c2.r) / (2*d);
  double dfr = c1.r*c1.r - rc*rc;

  if (EQ(dfr, 0.0)) dfr = 0.0;
  else if(dfr < 0.0) return ret;

  double rs = sqrt(dfr);
  Vec sgn = (c2.c - c1.c) / d;
  ret.emplace_back(c1.c + sgn*Point(rc, rs));
  if (dfr > 0.0) ret.emplace_back(c1.c + sgn*Point(rc, -rs));
  return ret;
}

// Note that ccw(a, b, c) != CCW when a, b, c are colinear
Poly GrahamScan(vector<Point> ps) {
  int k = 0;
  int n = ps.size();
  Poly ret(n*2);

  sort(ps.begin(), ps.end());
  for (int i=0; i<n; i++) {
    while (k > 1 && ccw(ret[k-2], ret[k-1], ps[i]) != CCW) k--;
    ret[k++] = ps[i];
  }

  int k_ = k;
  for (int i=n-1; i>=0; i--) {
    while (k > k_ && ccw(ret[k-2], ret[k-1], ps[i]) != CCW) k--;
    ret[k++] = ps[i];
  }

  ret.resize(k-1);
  return ret;
}

double CalcArea(Poly ps) {
  double ret = 0.0;
  for (int i=0; i<ps.size(); i++) {
    ret += cross(ps[i], ps[(i+1)%ps.size()]);
  }
  return ret/2.0;
}

bool IsConvex(Poly ps) {
  return GrahamScan(ps).size() == ps.size();
}

Geometory ContainsPoint(Poly poly, Point p) {
  bool in = false;
  int n = poly.size();
  for (int i=0; i<n; i++) {
    Point a = poly[i];
    Point b = poly[(i+1)%n];
    Vec u = a - p;
    Vec v = b - p;

    if (u.Y > v.Y) swap(u, v);

    double cr = cross(u, v);
    if (u.Y <= 0 && 0 < v.Y && cr > EPS) in ^= 1;
    if (IntersectSP({a, b}, p)) return ON_LINE;
  }

  if (in) return INSIDE;
  return OUTSIDE;
}

// Convex* requires the elements of ps to be arranged counter clockwise.
pair<int, int> ConvexDiameterApexes(Poly ps) {
#if DEBUG
  assert (IsConvex(ps));
#endif

  int n = ps.size();
  int is = 0;
  int js = 0;
  for (int i=1; i<n; i++) {
    if (ps[i].Y > ps[is].Y) is = i;
    if (ps[i].Y < ps[js].Y) js = i;
  }

  int maxi, maxj;
  double maxd = norm(ps[is]-ps[js]);
  int i = is;
  int j = js;
  do {
    Vec a = ps[i+1] - ps[i];
    Vec b = ps[j+1] - ps[j];
    if (cross(a, b) > -EPS) j = (j+1)%n;
    else i = (i+1)%n;

    double d = norm(ps[i]-ps[j]);
    if (d > maxd) {
      maxd = d;
      maxi = i;
      maxj = j;
    }
  } while (i != is || j != js);

  return make_pair(maxi, maxj);
}

Line ClosestPair(vector<Point> ps) {
  auto CompareY = [](const Point &a, const Point &b) {
    if (a.Y != b.Y) return a.Y < b.Y;
    return a.X < b.X;
  };

  function<Line(Point*,int)> Rec = [&Rec, &CompareY](Point *ps, int n) {
    if (n <= 1) return Line{Point(0, 0), Point(INF, INF)};
    
    int m = n/2;
    double x = ps[m].X;
    Line a = Rec(ps, m);
    Line b = Rec(ps+m, n-m);
    double mind = DistL(a);
    Line ret = a;
    if (DistL(b) < mind) {
      mind = DistL(b);
      ret = b;
    }

    sort(ps, ps+n, CompareY);
    vector<Point> qs;
    qs.reserve(n);
    for (int i=0; i<n; i++) {
      if (abs(ps[i].X - x) >= mind) continue;

      for (int j=0; j<qs.size(); j++) {
        Point p1 = ps[i];
        Point p2 = qs[qs.size()-1-j];
        if (p1.Y - p2.Y >= mind) break;

        double d = abs(p1-p2);
        if (mind > d) {
          mind = d;
          ret = Line{p1, p2};
        }
      }

      qs.emplace_back(ps[i]);
    }

    return ret;
  };

  int n = ps.size();
  assert (n >= 2);
  sort(ps.begin(), ps.end());
  return Rec(&ps[0], n);
}

// Convex* requires the elements of ps to be arranged counter clockwise.
// <left, right> or <upper, lower>
pair<Poly, Poly> CutConvex(Poly ps, Line l) {
#if DEBUG
  assert (IsConvex(ps));
#endif

  //if (l[0].Y > l[1].Y) swap(l[0], l[1]);
  //else if (EQ(l[0].Y, l[1].Y) && l[0].X > l[1].X) swap(l[0], l[1]);

  Poly left;
  Poly right;
  for (int i=0; i<ps.size(); i++) {
    Point a = ps[i];
    Point b = ps[(i+1)%ps.size()];

    if (ccw(l[0], l[1], a) != CW) left.emplace_back(a);
    else right.emplace_back(a);

    Line m{a, b};
    if (IntersectLS(l, m)) {
      Point p = CrossPointLL(l, m);
      left.emplace_back(p);
      right.emplace_back(p);
    }
  }

  return make_pair(left, right);
}

Circle Circum(Point a, Point b, Point c) {
  Circle ret{{INF, INF}, 0.0};
  Line l{a, b};
  Line m{b, c};
  Line lp = PerpendBisect(l);
  Line mp = PerpendBisect(m);
  if (IsParallel(lp, mp)) return ret;

  ret.c = CrossPointLL(lp, mp);
  ret.r = abs(a-ret.c);
  return ret;
}
int n;
Circle cs[114514];
double mind[400][400];
vector<Point> ps;

typedef pair<Point, int> Event;
vector<Event> es;

int main() {
  while (1) {
    scanf("%d", &n);
    if (n == 0) return 0;

    ps.clear();
    for (int i=0; i<n; i++) {
      int x, y;
      double r;
      scanf("%d%d%lf", &x, &y, &r);
      cs[i] = Circle{Point(x, y), r};
      ps.push_back(cs[i].c);
    }
  
    for (int i=1; i<n; i++) {
      vector<Point> cros = CrossPointCC(cs[i-1], cs[i]);
      assert (cros.size() == 2);
      ps.push_back(cros[0]);
      ps.push_back(cros[1]);
    }
    //sort(ps.begin(), ps.end());
  
    int m = ps.size();
    for (int i=0; i<m; i++) for (int j=0; j<m; j++) mind[i][j] = INF;
    for (int i=0; i<m; i++) {
      mind[i][i] = 0;
      for (int j=i+1; j<m; j++) {
        es.clear();

        //printf("consider %d %d %f %f %f %f\n", i, j, ps[i].X, ps[i].Y, ps[j].X, ps[j].Y);
        for (int k=0; k<n; k++) {
          vector<Point> cros = CrossPointCS(cs[k], Line{ps[i], ps[j]});
          if (cros.empty()) continue;
  
          if (cros.size() == 1) {
            double id = abs(ps[i]-cs[k].c);
            double jd = abs(ps[j]-cs[k].c);
            if (id < min(jd, cs[k].r)) cros.push_back(ps[i]);
            else if (jd < min(id, cs[k].r)) cros.push_back(ps[j]);
            else { 
              Point p = cros[0];
              cros.push_back(p);
            }
          }
  
          if (cros[1] < cros[0]) {
            swap(cros[0], cros[1]);
          }
  
          //printf("%f %f %f %f\n", cros[0].X, cros[0].Y, cros[1].X, cros[1].Y);
          es.push_back(Event(cros[0], -1));
          es.push_back(Event(cros[1], +1));
  
          Vec v1 = ps[i]-cs[k].c;
          Vec v2 = ps[j]-cs[k].c;
          if (EQ(abs(v1), cs[k].r) && EQ(abs(v2), cs[k].r)) {
            double ar = abs(arg(v2/v1)) * cs[k].r;
            double g = min(mind[i][j], ar);
            mind[i][j] = mind[j][i] = g;
          }
        }
  
        sort(es.begin(), es.end());
        int cnt = 0;
        bool fail = false;
        Point lim = Point(-INF, -INF);
        for (int idx=0; idx<es.size(); idx++) {
          Event &e = es[idx];
          Point p = e.first;
          //printf("%d: %f %f\n", idx, p.X, p.Y);
          if (idx == 0 && !EQ(p, min(ps[i], ps[j]))) {
            //printf("%f %f %f %f\n", min(ps[i], ps[j]).X, min(ps[i], ps[j]).Y, p.X, p.Y);
            
            fail = true;
            break;
          }

          cnt += e.second;
          lim = max(lim, p);
          if (cnt > 0 || (cnt == 0 && idx < es.size()-1)) {
            fail = true;
            break;
          }
          //printf("%d %d cnt: %d st: %d\n", i, j, cnt, fail);
        }
        //printf("%f %f\n", lim.X, lim.Y);
        if (!es.empty() && !EQ(lim, max(ps[i], ps[j]))) fail = true;
  
        if (!fail) {
          mind[i][j] = mind[j][i] = abs(ps[i]-ps[j]);
          //printf("connect %d %d %f\n", i, j, mind[i][j]);
        }
      }
    }
  
    for (int k=0; k<m; k++) {
      for (int i=0; i<m; i++) {
        for (int j=0; j<m; j++) {
          mind[i][j] = min(mind[i][j], mind[i][k]+mind[k][j]);
          //printf("mind %d %d %f\n", i, j, mind[i][j]);
        }
      }
    }
  
    //printf("ans: %.10f\n", mind[0][n-1]);
    printf("%.10f\n", mind[0][n-1]);
  }
}