import heapq
N,M = map(int,input().split())
X,Y = map(int,input().split())
X,Y = X-1,Y-1
lsP = []
for i in range(N):
    p,q = map(int,input().split())
    lsP.append((p,q))
lsG = [[] for i in range(N)]
for i in range(M):
    P,Q = map(int,input().split())
    P -= 1
    Q -= 1
    dist = ((lsP[P][0]-lsP[Q][0])**2+(lsP[P][1]-lsP[Q][1])**2)**(1/2)
    lsG[P].append((Q,dist))
    lsG[Q].append((P,dist))

used = [False]*(N)
inf = float('INF')
lscost = [inf]*(N)
lscost[X] = 0
h = [(0,X)]
while h:
    c,n = heapq.heappop(h)
    if used[n]:
        continue
    used[n] = True
    for j,cost in lsG[n]:
        if used[j]:
            continue
        if lscost[j] > lscost[n] + cost:
            lscost[j] = lscost[n] + cost
            heapq.heappush(h, (lscost[j],j))
print(lscost[Y])