#include <bits/stdc++.h>
#define ll long long
#define int long long
#define lb(x) ((x) & (-(x)))
#define pii pair<ll, ll>
#define pll pair<ll, ll>
#define st first
#define nd second
#define ld long double

using namespace std;

int read()
{
    int x = 0, c = 0;
    while('0' > c || c > '9')
        c = getchar();
    while('0' <= c && c <= '9')
        x = x * 10 + c - '0', c = getchar();
    return x;
}

const int maxn = 100005;

int n, m, s, t;
ll h[maxn];
vector <int> pic[maxn];
ll sps[maxn], spt[maxn];
priority_queue <pll, vector<pll>, greater<pll> > que;
int vis[maxn];

ll calc(int x, int y)
    {return (h[x] - h[y]) * (h[x] - h[y]);}

void dij(ll *sp, int s)
{
    que.push({0, s});
    while(que.size())
    {
        ll in = que.top().nd;
        que.pop();
        if(vis[in]) continue;
        vis[in] = 1;
        for(int i : pic[in])
        {
            if(!vis[i] && (!sp[i] || (sp[i] > sp[in] + calc(in, i))))
            {
                sp[i] = sp[in] + calc(in, i);
                que.push({sp[i], i});
            }
        }
    }
    memset(vis, 0, sizeof vis);
}

pair <ld, ld> q[maxn];
int l, r;
ld pnt[maxn];

ld getp(pair <ld, ld> a, pair <ld, ld> b)
{
    return (b.nd - a.nd) / (a.st - b.st);
}

ld getans(pair <ld, ld> l, ll x)
{
    return l.st * x + l.nd;
}

ld ans = 100000000000000000LL;

void sol(ll *a, ll *b)
{
    for(int i = 1; i <= n; i ++)
    {
        if(i == s || i == t)
            continue;
        l = 1, r = 0;
        for(int j : pic[i])
        {
            //cout<<j<<endl;
            while(r - l + 1 > 1 && pnt[l + 1] < h[j])
                l ++;
            if(r >= l) ans = min(ans, getans(q[l], h[j]) + 0.5 * h[j] * h[j] + b[j]);
            pair <ld, ld> lin = {-h[j], a[j] + 0.5 * h[j] * h[j]};
            while(r - l + 1 > 1)
            {
                int flag = 0;
                if(q[r].st == lin.st)
                {
                    flag = (lin.nd < q[r].nd);
                }
                else
                {
                    ld npt = getp(q[r], lin);
                    if(npt < pnt[r]) flag = 1;
                }
                if(flag) r --;
                else break;
            }
            q[++ r] = lin;
            pnt[r] = getp(lin, q[r - 1]);
        }
    }
}

bool _Cmp(int x, int y)
    {return h[x] < h[y];}

signed main()
{
    cin>>n>>m>>s>>t;
    for(int i = 1; i <= n; i ++)
        h[i] = read();
    for(int i = 1; i <= m; i ++)
    {
        int u = read();
        int v = read();
        pic[u].push_back(v);
        pic[v].push_back(u);
    }
    dij(sps, s);
    dij(spt, t);
    for(int i = 1; i <= n; i ++)
        sort(pic[i].begin(), pic[i].end(), _Cmp);
    for(int i : pic[s])
        ans = min(ans, (ld) spt[i]);
    for(int i : pic[t])
        ans = min(ans, (ld) sps[i]);
    //cout<<ans<<endl;
    sol(sps, spt);
    sol(spt, sps);
    cout<<ans<<endl;
}