import sequtils,strutils,math,heapqueue

type
    sen = tuple[b : int, d : float64 ]
    t = tuple[cost : float64, p : int]
var
    N, M : int
    X, Y : int
    p,q : int
    dentyuu = newSeq[array[2,int]](0)
    densen = newSeqWith(200010, newSeq[sen](0))
    hyou : array[200010, float64]
(N, M) = stdin.readline.split.map(parseInt)
(X, Y) = stdin.readline.split.map(parseInt)
X -= 1
Y -= 1

for n in 1..N:
    (p,q) = stdin.readline.split.map(parseInt)
    dentyuu.add([p, q])

for m in 1..M:
    (p, q) = stdin.readline.split.map(parseInt)
    p -= 1
    q -= 1
    var dx : float = (dentyuu[p][0] - dentyuu[q][0]).float
    var dy : float = (dentyuu[p][1] - dentyuu[q][1]).float
    dx = dx * dx
    dy = dy * dy
    var d = sqrt(dx + dy)
    var l : sen = (q, d)
    densen[p].add(l)
    l = (p, d)
    densen[q].add(l)

for i in 0..200000:
    hyou[i] = 1e10


var hp = initHeapQueue[t]()
var i : t = (0.0, X)
hp.push(i)

while true:
    var P = hp.pop()
    if hyou[P.p] < P.cost:
        continue
    if P.p == Y:
        break
    hyou[P.p] = P.cost
    for s in densen[P.p]:
        if hyou[s[0]] > s[1] + hyou[P.p]:
            hp.push((s[1] + hyou[P.p], s[0]))
            hyou[s[0]] = s[1] + hyou[P.p] 

echo hyou[Y]