#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using ld = long double;
const int N = 100005;
vector<int> adj[N];
ld h[N];
int n, m;


const ll INF = 1e16;
vector<ld> Dijkstra(int src) {
    vector<ld> dis(n, INF);
    vector<bool> vis(n, false);

    using pll = pair<ld, int>;
    priority_queue<pll, vector<pll>, greater<pll>> pq;

    dis[src] = 0;
    pq.push({0, src});
    while(!pq.empty()) {
        int x = pq.top().second;
        pq.pop();
        if(vis[x]) continue;

        vis[x] = true;
        for(auto v : adj[x]) {
            ll w = (h[v] - h[x]) * (h[v] - h[x]);
            if(dis[v] > dis[x] + w) {
                dis[v] = dis[x] + w;
                pq.push({dis[v], v});
            }
        }
    }
    return dis;
}

int main() {
    cin.tie(0);
    ios_base::sync_with_stdio(false);

    int s, t;
    cin >> n >> m >> s >> t;
    s--, t--;
    for(int i = 0; i < n; i++) {
        cin >> h[i];
    }
    
    for(int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--, b--;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }

    vector<ld> from_src = Dijkstra(s), to_dst = Dijkstra(t);

    ld ans = from_src[t];
    for(int i = 0; i < n; i++) {
        for(auto v : adj[i]) {
            for(auto u : adj[i]) {
                if(v == u) continue;
                ans = min(ans, from_src[v] + to_dst[u] + (h[v] * h[v]) / (ld)2.0 + (h[u] * h[u]) / (ld)2.0 - h[u] * h[v]);
            }
        }
    }

    cout << fixed << setprecision(20) << ans << "\n";
}