#include<bits/stdc++.h>
using namespace std;
#define lalala ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define endl "\n"
#define ll long long
#define pb push_back
#define uwu 100005
vector<pair<int,int>>adj[uwu];
double noiki(int N, int M, int K, int H, vector<int> x, vector<int>y, vector<int> c, vector<int> arr){int father[N];
for(int i=0;i<M;i++){
adj[x[i]].pb({y[i],c[i]});
adj[y[i]].pb({x[i],c[i]});
}
ll int yol[N];
for(int i=0;i<N;i++){
father[i]=-1;
yol[i]=1000000000000000000;
}
priority_queue<tuple<ll int,int,int>> pq;
pq.push({(ll int)0,0,-1});
while(pq.size()){
ll int node,once, deg;
tie(deg,node,once)=pq.top();deg=-deg;
pq.pop();
if(arr[node]==0){
deg=0;
}
if(yol[node]<=deg)continue;
yol[node]=deg;
father[node]=once;
if(node==H)continue;
for(auto u:adj[node]){
ll int kim=u.first, lira=u.second+deg;
pq.push({-lira,kim,node});
}
}
for(int i=0;i<N;i++)adj[i].clear();
if(yol[H]==1000000000000000000)yol[H]=-1;
return (1.0)*(double)yol[H];
}
double uc(int N, int M, int K, int H, vector<int> x, vector<int>y, vector<int> c, vector<int> arr){
int kim[3][3];
for(int i=0;i<M;i++){
adj[x[i]].pb({y[i],c[i]});
adj[y[i]].pb({x[i],c[i]});
}
for(int i=0;i<3;i++){for(int j=0;j<3;j++)kim[i][j]=1000000007;}
for(int i=0;i<M;i++){
kim[x[i]][y[i]]=min(kim[x[i]][y[i]],c[i]);
kim[y[i]][x[i]]=min(kim[y[i]][x[i]],c[i]);
}
double yol[N];
for(int i=0;i<N;i++){
yol[i]=1000000000000000000;
}
if(H==0)return 0;
if(N==3){
if(H==2&&kim[0][H]!=1000000007&&kim[0][1]==1000000007) return kim[0][H]/((arr[H]==2&&K)?2.0:1.0);
if(H==1&&kim[0][H]!=1000000007&&kim[0][2]==1000000007) return kim[0][H]/((arr[H]==2&&K)?2.0:1.0);
priority_queue<tuple<double,int,int>> pq;
pq.push({-0.0,0,0});
while(pq.size()){
int node,kac;double deg;
tie(deg,node,kac)=pq.top();deg=-deg;
pq.pop();
if(arr[node]==0)deg=0;
if(arr[node]==2&&kac<K){
deg=deg/2;
kac++;
}
if(yol[node]<=deg)continue;
yol[node]=deg;
if(node==H)continue;
for(auto u:adj[node]){
int ner=u.first;double lira=u.second+deg;
pq.push({-lira,ner,kac});
}
}
if(yol[H]==1000000000000000000)yol[H]=-1;
return yol[H];
}
if(N==2){
if(kim[0][H]==1000000007)return -1;
if(arr[H]==0)return 0;
if(arr[H]==2&&K)return kim[0][H]/2.0;
return kim[0][H];
}
}
double solve(int N, int M, int K, int H, vector<int> x, vector<int>y, vector<int> c, vector<int> arr){
int yes=0;
for(int i=0;i<N;i++){
if(arr[i]==2){
yes=1;break;
}
}
double cev;
if(yes==0)return noiki(N, M, K, H,x, y, c, arr);
if(N<=3) cev=uc(N, M, K, H,x, y, c, arr);
for(int i=0;i<N;i++)adj[i].clear();
return cev;
}
