#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 pil pair<int,ll>
#define pli pair<ll,int>
#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<pli,vt<pli>,greater<pli>> pq;
pq.push({0,st});
while(!pq.empty())
{
pli k=pq.top(); pq.pop();
int u = k.se;
ll 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;
vt<pll> a;
for(auto &[u,_]:ke[i]){
a.pb({h[u]*-2, h[u]*h[u] + G[u]*2});
}
sort(all(a)); reverse(all(a));
for(auto [x,y]:a) myCHT.add(line(x,y));
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;
}