#include <bits/stdc++.h>
using namespace std;
#ifdef MIKU
string dbmc = "\033[1;38;2;57;197;187m", dbrs = "\033[0m";
#define debug(x...) cout << dbmc << "[" << #x << "]: ", dout(x)
void dout() { cout << dbrs << endl; }
template <typename T, typename ...U>
void dout(T t, U ...u) { cout << t << (sizeof...(u) ? ", " : ""); dout(u...); }
#else
#define debug(...) 39
#endif
#define fs first
#define sc second
#define mp make_pair
#define FOR(i, j, k) for (int i = j, Z = k; i < Z; i++)
typedef pair<int, int> pii;
typedef pair<double, int> pli;
namespace {
const int MXN = 100005;
const double INF = 3.9e18;
int n, m, k, h;
vector<int> x, y, c, s;
vector<pli> edge[MXN];
vector<pli> sr;
double dis[MXN], ans;
priority_queue<pli, vector<pli>, greater<pli>> pq;
bitset<MXN> b;
void DFS(int id) {
debug(id);
b[id] = true;
if (s[id] == 0) sr.push_back(mp(0.0, id));
for (auto &[w, i] : edge[id]) {
if (b[i]) continue;
DFS(i);
}
}
double DIJKSTRA() {
fill(dis + 1, dis + n + 1, INF);
for (auto &i : sr) pq.push(i);
while (pq.size()) {
auto [len, id] = pq.top();
pq.pop();
if (dis[id] < INF) continue;
dis[id] = len;
for (auto &[w, i] : edge[id]) {
if (dis[i] < INF) continue;
pq.push(mp(w + len, i));
}
}
return dis[h];
}
double miku() {
FOR(i, 0, m) {
edge[x[i]].push_back(mp((double) c[i], y[i]));
edge[y[i]].push_back(mp((double) c[i], x[i]));
}
ans = INF;
sr.push_back(mp(0.0, 1));
DFS(1);
for (auto &[_, i] : sr) debug(i);
while (k--) {
ans = min(ans, DIJKSTRA());
sr.clear();
FOR(i, 1, n + 1) if (s[i] == 2) sr.push_back(mp(dis[i] / 2.0, i));
}
DIJKSTRA();
ans = min(ans, DIJKSTRA());
return ans;
}
void RESET() {
FOR(i, 1, n + 1) {
edge[i].clear();
b[i] = false;
}
}
}
double solve(int N, int M, int K, int H, vector<int> X, vector<int> Y, vector<int> C, vector<int> S) {
H++;
for (auto &i : X) i++;
for (auto &i : Y) i++;
S.insert(S.begin(), 0);
::n = N;
::m = M;
::k = K;
::h = H;
::x = X;
::y = Y;
::c = C;
::s = S;
double ans = miku();
RESET();
return (ans == ::INF ? -1.0 : ans);
}
#ifdef MIKU
int32_t main() {
cin.tie(0) -> sync_with_stdio(false);
cin.exceptions(cin.failbit);
int n, m, k, h;
vector<int> x, y, c, s;
cin >> n >> m >> k >> h;
x.resize(m);
y.resize(m);
c.resize(m);
s.resize(n);
for (auto &i : s) cin >> i;
FOR(i, 0, m) cin >> x[i] >> y[i] >> c[i];
double d = solve(n, m, k, h, x, y, c, s);
cout << d << '\n';
return 0;
}
#endif
