#include "cyberland.h"
// 赤コーダーになりたい
// お願い いいですか？
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
// Pragmas
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// Namespaces
using namespace std;
using namespace __gnu_pbds;
// Data types
using si = short int;
using ll = long long;
using lll = __int128;
using ld = long double;
// Pairs
using pii = pair<int, int>;
using psi = pair<si, si>;
using pll = pair<ll, ll>;
using plll = pair<lll, lll>;
using pld = pair<ld, ld>;
#define fi first
#define se second
// For
#define Frue(i, n, N) for (int i = (n); i <= (N); i++)
#define Fru(i, n, N) for (int i = (n); i < (N); i++)
#define Frde(i, n, N) for (int i = (n); i >= (N); i--)
#define Frd(i, n, N) for (int i = (n); i > (N); i--)
// PBDS
template<typename Z>
using ordered_set = tree<Z, null_type, less<Z>, rb_tree_tag, tree_order_statistics_node_update>;
// Various outputs
template<typename Y, typename Z> ostream& operator<<(ostream &os, const pair<Y, Z> &p) {
return os << '(' << p.fi << ',' << p.se << ')';
}
template<typename Z> ostream& operator<<(ostream &os, const vector<Z> &v) {
os << '{'; bool _first = 1;
for (auto &i : v) {if (!_first) os << ", "; os << i; _first = 0;}
return os << '}';
}
template<typename Z, unsigned long long sz> ostream& operator<<(ostream &os, const array<Z, sz> &arr) {
os << '{'; bool _first = 1;
for (auto &i : arr) {if (!_first) os << ", "; os << i; _first = 0;}
return os << '}';
}
// Quick macro functions
#define sqr(x) ((x)*(x))
#define debug(x) cout << #x << " = " << (x) << '\n'
#define debugV(v, x) cout << #v << "[" << (x) << "] = " << (v[x]) << '\n'
#define rrebug(x) cerr << #x << " = " << (x) << '\n'
#define rrebugV(v, x) cerr << #v << "[" << (x) << "] = " << (v[x]) << '\n'
#define All(x) x.begin(), x.end()
#define Sort(x) sort(All(x))
#define Reverse(x) reverse(All(x))
#define Uniqueify(x) Sort(x); x.erase(unique(All(x)), x.end())
#define RandomSeed chrono::steady_clock::now().time_since_epoch().count()
#define MultipleTestcases int _tc; cin >> _tc; for (int _cur_tc = 1; _cur_tc <= _tc; _cur_tc++)
// Check min and max
template<typename Z> void chmin(Z &a, Z b) {a = min(a, b);}
template<typename Z> void chmax(Z &a, Z b) {a = max(a, b);}
// Modular arithmetic
template<int MOD>
class ModInt {
public:
int v;
ModInt() : v(0) {}
ModInt(long long _v) {
v = int((-MOD < _v && _v < MOD) ? (_v) : (_v % MOD));
if (v < 0) v += MOD;
}
friend bool operator==(const ModInt &a, const ModInt &b) {return a.v == b.v;}
friend bool operator!=(const ModInt &a, const ModInt &b) {return a.v != b.v;}
friend bool operator< (const ModInt &a, const ModInt &b) {return a.v < b.v;}
friend bool operator<=(const ModInt &a, const ModInt &b) {return a.v <= b.v;}
friend bool operator> (const ModInt &a, const ModInt &b) {return a.v > b.v;}
friend bool operator>=(const ModInt &a, const ModInt &b) {return a.v >= b.v;}
ModInt &operator+=(const ModInt &a) {if ((v += a.v) >= MOD) v -= MOD; return *this;}
ModInt &operator-=(const ModInt &a) {if ((v -= a.v) < 0) v += MOD; return *this;}
ModInt &operator*=(const ModInt &a) {v = 1ll * v * a.v % MOD; return *this;}
ModInt &operator/=(const ModInt &a) {return (*this) *= inverse(a);}
friend ModInt pow(ModInt a, long long x) {
ModInt res = 1;
for (; x; x /= 2, a *= a) if (x & 1) res *= a;
return res;
}
friend ModInt inverse(ModInt a) {return pow(a, MOD - 2);}
ModInt operator+ () const {return ModInt( v);}
ModInt operator- () const {return ModInt(-v);}
ModInt operator++() const {return *this += 1;}
ModInt operator--() const {return *this -= 1;}
friend ModInt operator+(ModInt a, const ModInt &b) {return a += b;}
friend ModInt operator-(ModInt a, const ModInt &b) {return a -= b;}
friend ModInt operator*(ModInt a, const ModInt &b) {return a *= b;}
friend ModInt operator/(ModInt a, const ModInt &b) {return a /= b;}
friend istream &operator>>(istream &is, ModInt &v) {return is >> v.v;}
friend ostream &operator<<(ostream &os, const ModInt &v) {return os << v.v;}
};
const int ModA = 998244353;
const int ModC = 1e9 + 7;
using MintA = ModInt<ModA>;
using MintC = ModInt<ModC>;
// Other constants
const double INF = 1e18;
const double iINF = 1e9;
const double EPS = 1e-9;
const double iEPS = 1e-6;
const bool ge(double x, double y) {return ((x - y) >= EPS);}
const bool geq(double x, double y) {return ((x - y) >= -EPS);}
using pdi = pair<double, int>;
void Dijkstra(int N, vector<vector<pii>> &adj, vector<int> &start, vector<double> &dist) {
priority_queue<pdi, vector<pdi>, greater<pdi>> PQ;
vector<bool> vis(N, false);
for (auto i : start) PQ.push({dist[i], i});
while (!PQ.empty()) {
auto [cdist, cur] = PQ.top();
PQ.pop();
if (vis[cur]) continue;
vis[cur] = true;
for (auto &[nxt, w] : adj[cur]) {
if (ge(dist[nxt], dist[cur] + w)) {
dist[nxt] = dist[cur] + w;
PQ.push({dist[nxt], nxt});
}
}
}
}
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) {
K = max(K, 100);
vector<vector<pii>> adj(N, vector<pii>());
for (int i = 0; i < M; i++) {
adj[x[i]].push_back({y[i], c[i]});
adj[y[i]].push_back({x[i], c[i]});
}
adj[H].clear();
vector<int> stReach = {0};
vector<double> rd(N, INF);
rd[0] = 0;
Dijkstra(N, adj, stReach, rd);
vector<bool> reach(N, false);
for (int i = 0; i < N; i++) {
if (geq(rd[i], INF)) continue;
reach[i] = true;
}
vector<int> stInit = {0}, stDiv = {};
for (int i = 1; i < N; i++) {
if (arr[i] == 0 && reach[i]) stInit.push_back(i);
if (arr[i] == 2 && reach[i]) stDiv.push_back(i);
}
vector<double> dist(N, INF);
for (auto i : stInit) dist[i] = 0;
// K = 0
Dijkstra(N, adj, stInit, dist);
double ans = dist[H];
for (int i = 1; i <= K; i++) {
vector<double> nd(N, INF);
for (auto i : stDiv) {
if (geq(dist[i], INF)) continue;
double cur = dist[i] / 2;
// debug(cur);
for (auto &[nxt, w] : adj[i]) {
nd[nxt] = min(nd[nxt], cur + w);
}
}
swap(nd, dist);
// debug(dist);
Dijkstra(N, adj, stDiv, dist);
ans = min(ans, dist[H]);
}
if (geq(ans, INF)) ans = -1;
return ans;
}
#ifdef Zanite
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));
}
}
#endif
