//Serene
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<cmath>
#include<set>
using namespace std;
const int maxn=100+10;
double n,v;struct Node{double x,y;int pos;
}node[maxn];int fir[maxn],nxt[maxn*maxn],to[maxn*maxn],e=0;
double val[maxn*maxn];
void add(int x,int y,double z) {to[++e]=y;nxt[e]=fir[x];fir[x]=e; val[e]=z;
}bool cmp(const Node& a,const Node& b) {return a.x==b.x? a.y>b.y:a.x<b.x;
}double ds(int x,int y) {return sqrt((node[x].x-node[y].x)*(node[x].x-node[y].x)+(node[x].y-node[y].y)*(node[x].y-node[y].y));
}double ff(int x,int y) {return sqrt((node[x].y-node[y].y)/5.0);
}double dis[maxn];
int zz[maxn];
bool vis[maxn];
void spfa(int st) {memset(zz,0,sizeof(zz));memset(vis,0,sizeof(vis));for(int i=2;i<=n;++i) dis[i]=1e7;int s=1,t=0,x,y,z;zz[++t]=st;vis[st]=1;while(s<=t) {x=zz[s%maxn];for(y=fir[x];y;y=nxt[y]) {z=to[y];if(dis[z]<=dis[x]+val[y]) continue;dis[z]=dis[x]+val[y];if(!vis[z]) {vis[z]=1;t++;zz[t%maxn]=z;}}s++;vis[x]=0;}
}int main() {scanf("%lf%lf",&n,&v);int z;for(int i=1;i<=n;++i) {node[i].pos=i;scanf("%lf%lf",&node[i].x,&node[i].y);scanf("%d",&z);if(z)add(z,i,ds(z,i)/v),add(i,z,ds(z,i)/v);}sort(node+1,node+(int)n+1,cmp);for(int i=1;i<=n;++i) for(int j=i+1;j<=n&&node[j].x==node[i].x;++j) add(node[i].pos,node[j].pos,ff(i,j));spfa(1);printf("%.2lf",dis[(int)n]);return 0;
}