#include <bits/stdc++.h>
#define db double
using namespace std;
const db inf = 1e12;
const db mid = 2.0;
db solve(int N, int M, int K, int H, vector <int> x, vector <int> y, vector <int> c, vector <int> arr){
K = min(K, 100);
vector <vector <int>> adj(N);
for (int i = 0; i < M; ++ i) adj[x[i]].push_back(i), adj[y[i]].push_back(i);
vector <db> dp(N, inf);
dp[0] = 0.0; db ans = inf;
for (int loops = 0; loops <= K; ++ loops){
priority_queue <pair <db, int>> qu;
vector <db> rd(N, inf);
for (int u = 0; u < N; ++ u){
if (dp[u] == inf || (u > 0 && arr[u] == 1)) continue;
if (arr[u] == 0) rd[u] = 0.0;
qu.push({-dp[u] / mid, u});
}
while (qu.size()){
auto [du, u] = qu.top();
qu.pop(); du = -du;
if (u == H) continue;
for (int id : adj[u]){
int v = x[id] ^ y[id] ^ u;
if (rd[v] > du + c[id]){
rd[v] = du + c[id];
qu.push({-rd[v], v});
}
}
}
if (!loops && rd[H] == inf) break;
dp = rd;
ans = min(ans, dp[H]);
}
if (ans == inf) return -1;
return ans;
}
//void solve(){
// int N, M, K; cin >> N >> M >> K;
// int H; cin >> H;
// vector <int> arr(N); for (int i = 0; i < N; ++ i) cin >> arr[i];
// vector <int> x(M), y(M), z(M); for (int i = 0; i < M; ++ i) cin >> x[i] >> y[i] >> z[i];
// cout << fixed << setprecision(10) << solve(N, M, K, H, x, y, z, arr) << '\n';
//}
//
//int main(){
// freopen("cyberland.inp", "r", stdin);
// freopen("cyberland.out", "w", stdout);
//// ios_base::sync_with_stdio(0);
//// cin.tie(0);
//// cout.tie(0);
//
// int t = 1;
// while (t --) solve();
//
// return 0;
//}
