#include<bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(int i = a; i < b; i++)
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define int long long
#define double long double
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define endl '\n'

#ifdef NONTOI
#define debug(args...) LKJ("\033[1;32m["#args"]\033[0m", args)
template<class I> void LKJ(I&&x){ cerr << x << endl;}
template<class I, class...T> void LKJ(I&&x, T&&...t)
{ cerr << x << ", ", LKJ(t...); }
template<class I> void print(I a, I b)
{ while(a < b) cerr << *a << " \n"[next(a) == b], ++a;}
#else 
#define debug(...) ((void)0)
#define print(...) ((void)0)
#endif

int n, m, s, t, h[100010], dis1[100010], dis2[100010];
vector<int> g[100010];

struct Line {
    mutable ll k, m, p;
    bool operator<(const Line& o) const { return k < o.k; }
    bool operator<(ll x) const { return p < x; }
};

struct LineContainer : multiset<Line, less<>> {
    static const ll inf = LLONG_MAX;
    ll div(ll a, ll b) {
        return a / b - ((a ^ b) < 0 && a % b); }
    bool isect(iterator x, iterator y) {
        if(y == end()) return x->p = inf, 0;
        if(x->k == y->k) x->p = x -> m > y->m ? inf : -inf;
        else x->p = div(y->m - x->m, x->k - y->k);
        return x->p >= y->p;
    }
    void add(ll k, ll m) {
        auto z = insert({k, m, 0}), y = z++, x = y;
        while(isect(y, z)) z = erase(z);
        if(x != begin() && isect(--x, y)) isect(x, y = erase(y));
        while((y = x) != begin() && (--x)->p >= y->p)
            isect(x, erase(y));
    }
    ll query(ll x) {
        assert(!empty());
        auto l = *lower_bound(x);
        return l.k * x + l.m;
    }
};


signed main(){
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);
    cin >> n >> m >> s >> t;
    --s, --t;
    rep(i, 0, n) cin >> h[i];
    rep(i, 0, m){
        int x, y;
        cin >> x >> y;
        --x, --y;
        g[x].push_back(y);
        g[y].push_back(x);
    }
    priority_queue<pii, vector<pii>, greater<pii> > pq;
    rep(i, 0, n) dis1[i] = dis2[i] = 1e18;
    dis1[s] = 0;
    pq.push({0, s});
    while(!pq.empty()){
        pii pt = pq.top(); pq.pop();
        if(pt.first > dis1[pt.second]) continue;
        for(int u: g[pt.second]){
            if(dis1[u] > dis1[pt.second] + (h[pt.second] - h[u]) * (h[pt.second] - h[u])){
                dis1[u] = dis1[pt.second] + (h[pt.second] - h[u]) * (h[pt.second] - h[u]);
                pq.push({dis1[u], u});
            }
        }
    }
    dis2[t] = 0;
    pq.push({0, t});
    while(!pq.empty()){
        pii pt = pq.top(); pq.pop();
        if(pt.first > dis2[pt.second]) continue;
        for(int u: g[pt.second]){
            if(dis2[u] > dis2[pt.second] + (h[pt.second] - h[u]) * (h[pt.second] - h[u])){
                dis2[u] = dis2[pt.second] + (h[pt.second] - h[u]) * (h[pt.second] - h[u]);
                pq.push({dis2[u], u});
            }
        }
    }
    double ans = 1e18;
    rep(i, 0, n) ans = min(ans, (double)dis1[i] + dis2[i]);
    LineContainer lc;   
    rep(i, 0, n){
        lc.clear();
        if(i == s || i == t) continue;
        for(int j: g[i]){
            lc.add(h[j] * 2, -(h[j] * h[j] + 2 * dis1[j]));
        }
        for(int j: g[i]){
            int tmp = -lc.query(h[j]) + h[j] * h[j];
            double tmp1 = (double)tmp / (double)2;
            tmp1 += dis2[j];
            ans = min(ans, tmp1);
        }
    }
    for(int i: g[s]) ans = min(ans, (double)dis2[i]);
    for(int i: g[t]) ans = min(ans, (double)dis1[i]);
    cout <<fixed << setprecision(6) << ans << endl;

    return 0;
}