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;

const double EPS = 1e-8, PI = acos(-1);
inline bool eq(double a,double b){ return abs(b - a) < EPS; }
#define curr(P,i) P[i]
#define next(P,i) P[(i+1)%P.size()]
#define prev(P,i) P[(i+P.size()-1) % P.size()]
enum { OUT, ON, IN };

struct Geometory { // Geometory Library
  struct Point {
    double x, y;
    Point(){};
    Point(double x,double y):x(x),y(y){};
    Point operator+(const Point& b) const { return Point(x + b.x,y + b.y); }
    Point operator-(const Point& b) const { return Point(x - b.x,y - b.y); }
    Point operator*(const double b) const { return Point(x * b,y * b); }
    Point operator*(const Point& b) const { return Point(x * b.x - y * b.y,x * b.y + y * b.x); }
    Point operator/(const double b) const { return Point(x / b,y / b); }
    bool operator< (const Point& b) const { return x != b.x ? x < b.x : y < b.y; }
    bool operator==(const Point& b) const { return eq(x,b.x) && eq(y,b.y); }
    double norm(){ return x * x + y * y; }
    double arg(){ return atan2(x,y); }
    double abs(){ return sqrt(norm()); }
    Point rotate(double theta){ return Point(cos(theta) * x - sin(theta) * y,sin(theta) * x + cos(theta) * y); }
    Point rotate90(){ return Point(-y,x); }
    friend ostream& operator<<(ostream& os, Point& p){ return os<<"("<<p.x<<","<<p.y<<")"; }
    friend istream& operator>>(istream& is, Point& a){ return is>>a.x>>a.y; }
  };

  struct Line {
    Point a, b;
    Line(){};
    Line(Point a,Point b):a(a),b(b){};
  };
  struct Segment {
    Point a, b;
    Segment(){};
    Segment(Point a,Point b):a(a),b(b){};
  };
  struct Circle {
    Point p; double r;
    Circle(){};
    Circle(Point p, double r) : p(p),r(r){};
  };
  typedef vector< Point > Polygon;
  typedef vector< Segment > Segments;
  typedef vector< Line > Lines;
  typedef vector< Circle > Circles;
  typedef pair< Point, Point > PointPoint;

  double cross(const Point& a,const Point& b){
    return a.x * b.y - a.y * b.x;
  }
  double dot(const Point& a,const Point& b){
    return a.x * b.x + a.y * b.y;
  }

  int ccw(const Point& a,Point b,Point c){
    b = b - a, c = c - a;
    if(cross(b,c) > 0)    return +1;  // a → b で 反時計方向におれて c
    if(cross(b,c) < 0)    return -1; // a → b で 時計方向におれて c
    if(dot(b,c) < 0)      return +2;  // c -- a -- bで一直線上
    if(b.norm() < c.norm()) return -2; // a -- b -- cで一直線上
    return 0;  // a -- c -- bで一直線上
  }
  Point Projection(const Line& l, const Point& p){
    double t = dot( p - l.a, l.a - l.b) / (l.a - l.b).norm();
    return l.a + (l.a - l.b) * t;
  }
  Point Projection(const Segment& l, const Point& p){
    double t = dot( p - l.a, l.a - l.b) / (l.a - l.b).norm();
    return l.a + (l.a - l.b) * t;
  }
  Point Reflection(const Line& l, const Point& p){
    return p + (Projection( l, p) - p) * 2.0;
  }

  double Distance( const Line& l,const Point& p) { //OK
    return (p - Projection( l, p)).abs();
  }

  bool Intersect(const Line& l, const Line& m){
    return abs(cross(l.b - l.a, m.b - m.a)) > EPS || abs(cross(l.b-l.a, m.b-l.a)) < EPS;
  }
  bool Intersect(const Line& l, const Segment& s){
    return cross( l.b - l.a, s.a - l.a) * cross( l.b - l.a, s.b - l.a) < EPS;
  }
  bool Intersect(const Line& l, const Point& p){
    return abs(ccw(l.a, l.b, p)) != -1;
  }
  bool Intersect(const Segment& s, const Segment& t){
    return ccw(s.a, s.b, t.a) * ccw(s.a, s.b, t.b) <= 0 && ccw(t.a, t.b, s.a) * ccw(t.a, t.b, s.b) <= 0;
  }
  bool Intersect(const Segment& s, const Point& p){
    return ccw(s.a, s.b, p) == 0;
  }
  bool Intersect(const Circle& c,const Line& l){
    return Distance( l, c.p) <= c.r + EPS;
  }
  bool Intersect(const Circle& c,const Point& p){
    return abs( ( p - c.p).abs() - c.r ) < EPS;
  }
  int Intersect(const Circle& c, const Segment& l){
    if( (Projection( l, c.p) - c.p).norm() - c.r * c.r > EPS) return 0;
    const double d1 = ( c.p - l.a).abs(), d2 = ( c.p - l.b).abs();
    if( d1 < c.r + EPS && d2 < c.r + EPS) return 0;
    if( d1 < c.r - EPS && d2 > c.r + EPS || d1 > c.r + EPS && d2 < c.r - EPS ) return 1;
    const Point h = Projection( l, c.p);
    if( dot( l.a - h, l.b - h) < 0) return 2;
    return 0;
  }
  bool Intersect(const Circle& a,const Circle& b){
    return ( ( a.p - b.p).norm() - ( a.r + b.r) * ( a.r + b.r) < EPS) &&
      ( ( a.p - b.p).norm() - ( a.r - b.r) * ( a.r - b.r) > -EPS);
  }
  double Distance(const Segment& s,const Point& p){
    Point r = Projection(s, p);
    if ( Intersect( s, r)) return ( r - p).abs();
    return min( ( s.a - p).abs(), ( s.a - p).abs());
  }
  double Distance(const Segment& a,const Segment& b){
    if(Intersect( a, b)) return 0;
    return min( min( Distance( a, b.a), Distance( a, b.b)), min( Distance( b, a.a), Distance( b, a.b)));
  }
  double Distance(const Line& l,const Line& m) {
    return Intersect( l, m) ? 0 : Distance( l, m.a);
  }
  double Distance(const Line& l,const Segment& s) { //OK
    if (Intersect(l, s)) return 0;
    return min(Distance(l, s.a), Distance(l, s.b));
  }
  double Distance(const Point& a,const Point& b){ //OK
    return ( a - b).abs();
  }
  Point Crosspoint(const Segment& l,const Segment& m) { //OK
    double A = cross(l.b - l.a, m.b - m.a);
    double B = cross(l.b - l.a, l.b - m.a);
    if (abs(A) < EPS && abs(B) < EPS) return m.a; // same line
    return m.a + (m.b - m.a) * B / A;
  }
  PointPoint Crosspoint(const Circle& c,const Line l){
    Point hp = Projection( l, c.p), h =  hp - c.p;
    const double d2 = h.norm();
    Point v = ( l.b - l.a) * sqrt( c.r * c.r - d2) / ( l.b - l.a).abs();
    return PointPoint(hp - v, hp + v);
  }
  PointPoint Crosspoint(const Circle& c,const Segment& l) {
    Line aa = Line( l.a, l.b);
    if(Intersect(c, l) == 2) return Crosspoint(c, aa);
    PointPoint ret = Crosspoint(c, aa);
    if(dot(l.a - ret.first, l.b - ret.first) < 0) ret.second = ret.first;
    else ret.first = ret.second;
    return ret;
  }
  PointPoint Crosspoint(const Circle& c1,const Circle& c2){ //OK
    double d = (c1.p - c2.p).abs();
    double s = (c1.r + c2.r + d) / 2;
    double S = sqrt( s * ( s - c1.r) * ( s - c2.r) * ( s - d));
    double h = 2 * S / d;
    Point v = ( c2.p - c1.p) / ( c2.p - c1.p).abs();
    double m = sqrt( c1.r * c1.r - h * h);
    return PointPoint( c1.p + v * m + Point(0,1) * h * v, c1.p + v * m - Point(0,1) * h * v);
  }
  bool parallel(const Segment& a,const Segment& b){
  return abs( cross( a.b - a.a, b.b - b.a)) < EPS;
  }
  bool orthogonal(const Segment& a,const Segment& b){
    return dot( a.a - a.b, b.a - b.b) < EPS;
  }
  int Contains(const Polygon& Q,const Point& p){
    bool in = false;
    for(int i = 0 ; i < Q.size() ; i++ ){
      Point a = curr(Q,i) - p, b = next(Q,i) - p;
      if(a.y > b.y) swap(a,b);
      if(a.y <= 0 && 0 < b.y && cross(a,b) < 0) in = !in;
      if(cross(a,b) == 0 && dot(a,b) <= 0) return ON;
    }
    return in ? IN : OUT;
  }
  bool Contains(const Circle& c,const Point& p){
    return ( c.p - p).abs() < c.r + EPS;
  }
  double Area2(const Polygon& p){ //OK
    double A = 0;
    for (int i = 0; i < p.size(); ++i){
      A += cross(curr(p, i), next(p, i));
    }
    return A;
  }
};

Geometory geo;
typedef Geometory::Point P;
typedef Geometory::Line L;
typedef Geometory::Segment S;
typedef Geometory::Circle C;
struct node{
  double cost;
  P pos;
  int nowy, nowx;
  bool operator < (const node &left) const {
    return cost > left.cost;
  }
};

int main(){
  int n;
  C prev, now;

  Geometory::Segments seg;

  while(cin >> n, n){
    cin >> prev.p >> prev.r;
    seg.push_back( S( prev.p, prev.p));
    for(int i = 1; i < n; i++){
      cin >> now.p >> now.r;
      Geometory::PointPoint pp = geo.Crosspoint( prev, now);
      seg.push_back( S(pp.first,pp.second));
      prev = now;
    }
    seg.push_back( S( prev.p, prev.p));

    typedef pair< int, int > POS;
    typedef pair< double, P > PS;
    priority_queue< node > que;
    que.push((node){ 0, seg[0].a, 0, 0});
    bool used[101][2] = {{}};
    double ret;
    while(!que.empty()){
      node p = que.top(); que.pop();
      if(p.nowy == n){ ret = p.cost; break; }
      if(used[p.nowy][p.nowx]++) continue;
      for(int i = p.nowy + 1; i <= n; i++){
        S s1 = S( p.pos, seg[i].a), s2 = S( p.pos, seg[i].b);
        bool flag1 = true, flag2 = true;
        for(int j = i - 1; j > p.nowy; j--){
          if(!geo.Intersect( s1, seg[j])){
            flag1 = false;
            break;
          }
        }
        for(int j = i - 1; j > p.nowy; j--){
          if(!geo.Intersect( s2, seg[j])){
            flag2 = false;
            break;
          }
        }
        if(flag1) que.push((node){ p.cost + (s1.a - s1.b).abs(), s1.b, i, 0});
        if(flag2) que.push((node){ p.cost + (s2.a - s2.b).abs(), s2.b, i, 1});
      }
    }
    cout << fixed << setprecision(7) << ret << endl;

    seg.clear();
  }
}