#include <bits/stdc++.h>
using namespace std ;
#define ll long long
// #define test
#ifndef test
#include "cyberland.h"
#endif
////////////////////////////////////////////////////////////////////////
#include <vector>
double dist[100003][103] ;
vector <pair<int,int>> adj[100003] ;
bool v[100003] ;
void dfs(int x){
v[x]=1 ;
for (auto [a,l] : adj[x]) if (!v[a]) dfs(a) ;
}
double solve(int N, int M, int K, int H, std::vector<int> X, std::vector<int> Y, std::vector<int> C, std::vector<int> arr) {
int i,j ;
for (i = 0 ; i < N ; i ++){
v[i]=0 ;
adj[i].clear() ;
for (j = 0 ; j < 103 ; j ++) dist[i][j]=LLONG_MAX/2ll ;
}
for (i = 0 ; i < M ; i ++){
adj[X[i]].push_back({Y[i],C[i]}) ;
adj[Y[i]].push_back({X[i],C[i]}) ;
}
priority_queue <tuple<int,double,int>,vector<tuple<int,double,int>>,greater<tuple<int,double,int>>> q ;
dfs(0) ;
q.push({0,0,0}) ;
for (i = 1 ; i < N ; i ++) if (v[i]&&arr[i]==0) q.push({0,0,i}) ;
K=min(K,100) ;
while (!q.empty()){
auto [y,d,x]=q.top() ;
q.pop() ;
if (dist[x][y]<=d) continue ;
dist[x][y]=d ;
if (arr[x]==2){
if (y+1<=K&&d/2.0<dist[x][y+1]){
q.push({y+1,d/2.0,x}) ;
}
}
if (x!=H) for (auto [a,l] : adj[x]){
if (d+l<dist[a][y]) q.push({y,d+l,a}) ;
}
}
double mn=LLONG_MAX/2ll ;
for (i = 0 ; i <= K ; i ++) mn=min(mn,dist[H][i]) ;
if (mn!=LLONG_MAX/2ll) return mn ;
return -1;
}
////////////////////////////////////////////////////////////////////////
#ifdef test
//grader{
#include <cassert>
#include <cstdio>
#include <vector>
int main() {
int T;
assert(1 == scanf("%d", &T));
while (T--){
int N,M,K,H;
assert(4 == scanf("%d %d %d\n%d", &N, &M, &K, &H));
std::vector<int> x(M);
std::vector<int> y(M);
std::vector<int> c(M);
std::vector<int> arr(N);
for (int i=0;i<N;i++)
assert(1 == scanf("%d", &arr[i]));
for (int i=0;i<M;i++)
assert(3 == scanf("%d %d %d", &x[i], &y[i], &c[i]));
printf("%.12lf\n", solve(N, M, K, H, x, y, c, arr));
}
}
//grader}
#endif
