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 int dx[]={0,1,0,-1,1,-1,-1,1};
const int dy[]={-1,0,1,0,1,1,-1,-1};
const int INF = 1<<30;
const double EPS = 1e-15;
#define PB push_back
#define mk make_pair
#define fi first
#define se second
#define ll long long
#define reps(i,j,k) for(int i = (j); i < (k); i++)
#define rep(i,j) reps(i,0,j)
#define MOD 1000000007
typedef pair<int,int> Pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
struct Point{
    double x,y;
    Point(){}
    Point(double _x,double _y){
        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(k*x,k*y);
    }
     
    Point operator * (Point p){
        return Point(p.x*x-p.y*y,p.x*y+p.y*x);
    }

    Point operator / (double k){
        return Point(x/k,y/k);
    }
    
    Point operator = (Point p){
        x = p.x;
        y = p.y;
        return *this;
    }

    bool operator<(const Point &p)const{
        return x!=p.x?x<p.x:y<p.y;
    }

};
double dot(Point p, Point q){
    return p.x*q.x+p.y*q.y;
}
  
double cross(Point p,Point q){
    return p.x*q.y-q.x*p.y;
}
  
double norm(Point p){
    //?????????????????§?????????2???
    return p.x*p.x+p.y*p.y;
}
  
double pabs(Point p){
    //?????????????????§??????
    return sqrt(norm(p));
}
Point UnitVector(Point a){
    //??????????????????
    return a/pabs(a);
}
typedef vector<Point> Polygon;
struct Line : Polygon{
    Line(){}
    Line(Point p,Point q){
        PB(p);
        PB(q);  
    }
};
struct Circle{
    Point p; //?????????
    double r; //??????
    Circle(){}
    Circle(Point _p,double _r){
        p = _p;
        r = _r;
    }
};
int ccw(Point a,Point b,Point c){
    b = b-a;
    c = c-a;
    if(cross(b,c) > 0)return +1; //a???b ??§???????¨?????????????c ccw
    if(cross(b,c) < 0)return -1; //a???b ??§????¨?????????????c ccw
    if(dot(b,c) < 0)return +2; // c--a--b;
    if(pabs(b)<pabs(c))return -2; //a--b--c
    return 0; //a--c--b
}

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

Point reflection(Line l, Point p){
    return p + (projection(l,p)-p)*2.0; 
}

bool intersectSS(Line l,Line m){
    //l??¨m??????????????????????????????
    return (ccw(l[0],l[1],m[0])*ccw(l[0],l[1],m[1])<EPS)&&
            (ccw(m[0],m[1],l[0])*ccw(m[0],m[1],l[1])<EPS);
}

bool intersectSP(Line l, Point p){
    //??????l??¨???p?????????????????????
    return !ccw(l[0],l[1],p);
}

double distanceLP(Line l,Point p){
    //??????l??¨???p????????¢
    p = p - l[0];
    l[1] = l[1] - l[0];
    if(intersectSP(l,p))return 0.0;
    return fabs(cross(p,l[1])/pabs(l[1]));
}

bool intersectLL(Line l,Line m){
    return fabs(cross(l[1]-l[0],m[1]-m[0])) > EPS || //????????§??????
            fabs(cross(l[1]-l[0],m[0]-l[0])) < EPS; //????????????
}

bool intersectCP(Circle c,Point p){
    //???c??¨???p???????????????
    //true->???c????????¨??????p????????¨????????????.
    return fabs(pabs(p-c.p)-c.r)<EPS;
}

int intersectCL(Circle c,Line l,Point *p,Point *q){
    if(norm(projection(l,c.p) - c.p) - c.r*c.r > EPS)return 0;
    double d1 = pabs(c.p-l[0]);
    double d2 = pabs(c.p-l[1]);
    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;
    Point h = projection(l,c.p);
    if(dot(l[0] - h,l[1] - h) < 0)return 2;
    return 0;
}

int intersectCC(Circle a,Circle b,Point *p,Point *q){
    double dist = pabs(a.p-b.p);
    if(dist < fabs(a.r-b.r) || dist > a.r+b.r){
        //????????????????????´??????????????¨???
        //????????????????????¨???????????¨???
        *p = Point(1e15,1e15);
        *q = Point(1e15,1e15);
        return 0;
    }
    else if(fabs(dist-a.r-b.r) < EPS){
        //??????1?????§????????£???????????¨???
        Point way;
        way = b.p-a.p;
        *p = a.p+UnitVector(way)*a.r;
        *q = *p;
        return 1;
    }
    else{
        //??????2?????§????????£???????????¨???
        if(a.r < b.r){
            swap(a.r,b.r);
            swap(a.p,b.p);
        }
        double s = (a.r + b.r + dist) / 2.0 ;
        double area = sqrt(s * (s - a.r) * (s - b.r) * (s - dist));
        double h = 2.0 * area / dist;

        Point  v = b.p-a.p;
        v = UnitVector(v);
        Point  m = a.p + (v*sqrt(a.r*a.r-h*h));
        Point  n = v * Point(0.0,1.0);
        
        *p = m + (n * h);
        *q = m - (n * h);
        return 2;
    }
}

double TriangleArea(Point a,Point b,Point c){
    b = b - a;
    c = c - a;
    return cross(b,c)*0.5; //?????????????????¨??????????????§??¨???
}
 
double VertexArea(Polygon v){
    double subArea = 0.0;
    rep(i,v.size()-1){
        subArea += TriangleArea(v[0],v[i],v[i+1]);
    }
    return subArea; //?????????????????¨??????????????§??¨???
}

Point crosspoint(Line l,Line m){
    //??????l??¨??????m?????????
    if(intersectSS(l,m) == false)return Point(INF,INF);
    return m[0]+(m[1]-m[0])*cross(l[1]-l[0],l[1]-m[0])/cross(l[1]-l[0],m[1]-m[0]);
}
 
Polygon ConvexHull(Polygon v){
    //??????????????????
    int n = v.size();
    int k = 0;
    sort(v.begin(),v.end());
    Polygon e(2*n);
    for(int i=0;i<n;e[k++]=v[i++])
        while(k>=2&&ccw(e[k-2],e[k-1],v[i])<=0)k--;
    for(int i=n-2,t=k+1;i>=0;e[k++]=v[i--])
        while(k>=t&&ccw(e[k-2],e[k-1],v[i])<=0)k--;
    e.resize(k-1);
    return e;
}

struct edge
{
    int to;
    double cost;
    edge(){}
    edge(int _to,double _cost){
        to = _to;
        cost = _cost;
    }
    bool operator < (const edge &a)const{
        return a.cost<cost;
    }
};
typedef pair<Point,int> P;

int main(){
    int N;
    while(scanf("%d",&N),N){
        Circle C[128];
        vector < pair < Point , int >  > points;
        Point start,goal;
        rep(i,N){
            double x,y,r;
            scanf("%lf%lf%lf",&x,&y,&r);
            if(i == 0){
                start = Point(x,y);
            }
            if(i == N-1){
                goal = Point(x,y);
            }
            C[i] = Circle(Point(x,y),r);
        }
        vector < Line > arc;
        points.PB(P(start,0));
        rep(i,N){
            reps(j,i+1,N){
                Point p,q;
                int tmp = intersectCC(C[i],C[j],&p,&q);
                if(tmp > 0){
                    points.PB(P(p,j));
                    points.PB(P(q,j));
                    Line l;
                    l.PB(p);l.PB(q);
                    arc.PB(l);
         //         cout << p.x << " " << p.y << "\n";
         //         cout << q.x << " " << q.y << "\n";
                }
            }
        }
       // puts("$$$$$$$$$$$$$$$$$$$$$$");
        points.PB(P(goal,N-1));
        int goal_ID = points.size()-1;

        vector< edge > G[250];
        rep(i,points.size()){
            reps(j,i+1,points.size()){
                double dist = pabs(points[i].fi-points[j].fi);
                Line l;
                l.PB(points[i].fi);
                l.PB(points[j].fi);
                int cnt = 0;
                Point p,q;
                bool flg = true;
        //        cout << "&" <<points[i].se+1 << " " << points[j].se << "\n";
                for(int k = points[i].se+1; k < points[j].se+1; k++){
                    bool a = true;
                    a = intersectSS(l,arc[k-1]);
                    //cout << a << "\n";
                    if(!a){
                        flg = false;
                    }
                }
                if(!flg)continue;
                G[i].PB(edge(j,dist));
                G[j].PB(edge(i,dist));
            //    cout << i << " " << j << " " << dist << " "<< flg <<"\n";
            }
        }

        double d[250];
        fill(d,d+250,INF);
        priority_queue < edge > Q;
        Q.push(edge(0,0.0));

        while(!Q.empty()){
            edge e = Q.top();Q.pop();
            if(d[e.to] != INF)continue;
            d[e.to] = e.cost;
            rep(i,G[e.to].size()){
                Q.push(edge(G[e.to][i].to,G[e.to][i].cost+d[e.to]));
            }
        }

        printf("%.4lf\n",d[goal_ID]);
    }
    return 0;
}