#pragma GCC optimize ("O3")

//#incluse <bits/stdc++.h>

#include <iostream>     // Input/output stream objects
#include <fstream>      // File stream objects
#include <sstream>      // String stream objects
#include <iomanip>      // Input/output manipulators
#include <string>       // String class and functions
#include <vector>       // Dynamic array
#include <list>         // Doubly linked list
#include <set>          // Set container
#include <map>          // Map container
#include <queue>        // Queue container
#include <stack>        // Stack container
#include <algorithm>    // Algorithms on sequences (e.g., sort, find)
#include <cmath>        // Mathematical functions
#include <ctime>        // Date and time functions
#include <cstdlib>      // General purpose functions (e.g., memory management)
#include <cstring>      // C-style string functions
#include <cctype>       // Character classification functions
#include <cassert>      // Assert function for debugging
#include <exception>    // Standard exceptions
#include <functional>   // Function objects
#include <iterator>     // Iterator classes
#include <limits>       // Numeric limits
#include <locale>       // Localization and internationalization
#include <numeric>      // Numeric operations (e.g., accumulate)
#include <random>       // Random number generators
#include <stdexcept>    // Standard exception classes
#include <typeinfo>     // Runtime type information
#include <utility>      // Utility components (e.g., std::pair)
#include <tuple>
#include <cstdio>
#include <bitset>

using namespace std;

// ************ Setting up  ************
#define FPTU ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define TIME  (1.0 * clock() / CLOCKS_PER_SEC)
#define BUG(x) {cerr << #x << " = " << x << endl;}
#define pii pair<int,int>
#define pip pair<int,pii>
#define ppi pair<pii,int>
#define ll  long long
#define ull unsigned long long
#define usi unsigned int
#define pll pair<ll,ll>
#define plp pair<ll,pll>
#define ppl pair<pll,ll>
#define ppp pair<pii,pii>
#define oo 1000111000
#define ooo 1000111000111000111
#define inf 0x3f //4557430888798830399
#define fi first
#define se second
#define vt vector
#define pb push_back
#define all(arr) arr.begin(),arr.end()
#define bit(n, i) (((n) >> (i)) & 1)
#define db(x) cerr << #x << " = " << (x) << '\n';

ll rand_num(ll a,ll b) {
    random_device rd; mt19937 mt(rd()); uniform_int_distribution<ll> dist(a,b);
    return dist(mt);
}

int mod=1e9+7; // MODDDDDDDDDDDDD

template <typename T> void minimize(T &a, T b){ if(a>b)  a=b; }
template <typename T> void maximize(T &a, T b){ if(a<b)  a=b; }
template <typename T> void add(T &a, T b){ a+=b; if(a>=mod) a-=mod; }
template <typename T> T gcd(T a, T b){
    while(a!=0&&b!=0) if(a>b) a%=b; else b%=a; return a+b; }
void read_file()
{
    freopen("sample.inp","r",stdin);
    freopen("sample.out","w",stdout);
}
// =========> <3 VietHai1709 <3  <=========
struct line{
    ll a,b;
    line(ll x=0,ll y=-ooo)
    {
        a=x; b=y;
    }
    ll get(ll x)
    {
        return a*x+b;
    }
};
struct ConvextHullTrick{
    int n;
    int flag;
    vt<line> Line;
    ConvextHullTrick(){
        n=0;
        flag=0;
        Line.clear();
    }
    bool bad(line u,line v,line w)
    {
        return (double)(u.b-w.b)/(w.a-u.a)<=(double)(u.b-v.b)/(v.a-u.a);
        //return (u.b-w.b)*(v.m-u.m)<=(u.b-v.b)*(w.m-u.m);
    }
    void add(line L)
    {
        while(n>=2 && bad(Line[n-2],Line[n-1],L))
        {
            Line.pop_back();
            n--;
        }
        Line.pb(L);
        n++;
    }
    ll query(ll x)
    {
        if(flag>n-1) flag=n-1;
        while(flag+1<n && Line[flag].get(x)>Line[flag+1].get(x)) flag++;
        return Line[flag].get(x);
    }
};

void Dijktra(int st,vt<vt<pair<int,ll>>> Edge, vt<ll> &dis)
{
    dis[st]=0;
    priority_queue<pii,vt<pii>,greater<pii>> pq;
    pq.push({0,st});
    while(!pq.empty())
    {
        pii k=pq.top(); pq.pop();
        int u = k.se, w = k.fi;
        
        if (w > dis[u]) continue;

        for(auto &[v,x]: Edge[u]) {
           if (dis[v] > w + x) {
               dis[v] = x + w;
               pq.push({dis[v], v});
           }
        }
    }
}
ll dis(ll a,ll b){
    return (a-b)*(a-b);
}
bool cmp(pair<int,ll> &a, pair<int,ll> &b){
    return a.se<b.se;
}
void Minnnnnnn()
{
    int n,m,s,t;
    cin>>n>>m>>s>>t;
    vt<ll> h(n+1);
    for(int i=1;i<=n;i++) cin>>h[i];
    vt<vt<pair<int,ll>> > ke(n+1);
    while(m--){
        int u,v;
        cin>>u>>v;
        ll w=dis(h[u],h[v]);
        ke[u].pb({v,w});
        ke[v].pb({u,w});
    }
    vt<ll> F(n+1,ooo);
    vt<ll> G(n+1,ooo);
    Dijktra(s, ke, F);
    Dijktra(t, ke, G);
    
    ll ans=ooo;
    for(auto &[u,_]:ke[s]) ans=min(ans,G[u]*2);
    for(auto &[u,_]:ke[t]) ans=min(ans,F[u]*2);
    //cout<<setprecision(2)<<fixed<<ans/2.0<<'\n';
    for(int i=1;i<=n;i++) if(i!=s && i!=t){
        ConvextHullTrick myCHT;
        sort(all(ke[i]),cmp);reverse(all(ke[i]));
        for(auto &[u,_]:ke[i]){
            myCHT.add(line(h[u]*-2, h[u]*h[u] + G[u]*2));
        }
        for(auto &[u,_]:ke[i]){
            ans=min(ans, F[u]*2+h[u]*h[u]+myCHT.query(h[u]));
        }
    }
    cout<<setprecision(2)<<fixed<<ans/2.0;
}


int main(){
    
    FPTU; //fast
   // read_file();
    
    int __=1;
    //cin>>__;
    for(int _=1;_<=__;_++)
    {
        Minnnnnnn();
    }
    cerr << "Time elapsed: " << TIME << " s.\n";

    return 0;
}