#include <bits/stdc++.h>
using namespace std;
 
#ifdef DEBUG
#include "../Library/debug.h"
#else
#define dbg(x...)
#endif
 
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl; 
 
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define F0R(i, a) for (int i = 0; i < (a); ++i)
#define FORd(i, a, b) for (int i = (b) - 1; i >= (a); --i)
#define F0Rd(i, a) for (int i = (a) - 1; i >= 0; --i)
#define trav(a, x) for (auto& a : x)
#define f first 
#define s second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
 
const char nl = '\n';
const int INF = 1e9;
const int MOD = 1e9 + 7;
struct DSU {
    vector<int> par, sz;
    int c; // connected components
    DSU(int n) : par(n), c(n) {
        sz.resize(n, 1); 
        for (int i = 0; i < n; ++i) par[i] = i;
    }
    int find(int i) {
        return par[i] == i ? i : (par[i] = find(par[i]));
    }
    bool same(int i, int j) {
        return find(i) == find(j);
    }
    int get_size(int i) {
        return sz[find(i)];
    }
    int count() {
        return c;
    }
    int merge(int i, int j) {
        if ((i = find(i)) == (j = find(j))) return -1;
        else --c;
        if (sz[i] > sz[j]) swap(i, j);
        par[i] = j;
        sz[j] += sz[i];
        return j;
    }
};
double solve(int n,int m,int k,int h,vi x,vi y,vi c,vi arr){
    vector<vpi> adj(n);
    k=min(k,70);
    DSU dsu(n);
    F0R(i,m){
        if(x[i]!=h&&y[i]!=h)
            dsu.merge(x[i],y[i]);
        adj[x[i]].pb({y[i],c[i]});
        adj[y[i]].pb({x[i],c[i]});
    }
    using T = tuple<double,int,int>;
    priority_queue<T,vector<T>,greater<T>>pq;
    vector<vector<double>> dist(k+1,vector<double>(n, 1e18));
    dist[0][0]=0;
    pq.push({0,0,0});
    F0R(i,n){
        if(arr[i]==0 && dsu.same(i,0)){
            pq.push({0,1,i});
            dist[1][i]=0;
        }
    }
    // if(!dsu.same(0,h))
    //     return -1;
    auto f=[&](double d, int k, int v){
        if(d < dist[k][v]){
            dist[k][v]=d;
            dbg(d,k,v)
            pq.push({d,k,v});
        }
    };
    vector<double> res(k,1e18);
    while(!pq.empty()){
        auto [w,_k,v]=pq.top();
        dbg(w,_k,v)
        pq.pop();
        if(dist[_k][v] < w)
            continue;
        if(v==h){
            // return w;
            res[_k]=min(w,res[_k]);
            continue;
        }
        for(auto [u,_w]:adj[v]){
            f(w+_w,_k,u);
            // if(arr[v]==0&&_k<k)
            //     f(0+_w,_k+1,u);
            if(arr[v]==2&&_k<k)
                f(w/2.0+_w,_k+1,u);
        }
    }
    double ans=*min_element(all(res));
    return ans==1e18?-1:ans;
}
 
// #define DEBUG
#ifdef DEBUG
int32_t main(){
    ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
    
    int TC = 1;
    // cin >> TC;
    while(TC--){
        int n,m,k,h;
        cin>>n>>m>>k>>h;
        vi x(m),y(m),c(m),arr(n);
        F0R(i,m)cin>>x[i];
        F0R(i,m)cin>>y[i];
        F0R(i,m)cin>>c[i];
        F0R(i,n)cin>>arr[i];
        cout<<solve(n,m,k,h,x,y,c,arr)<<nl;
    }
    return 0;
}
#endif
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