import heapq
N,M = map(int, input().split())
X,Y = map(int, input().split())
L = [[int(l) for l in input().split()] for _ in range(N)]
E = [[] for _ in range(N)]
for _ in range(M):
    p,q = map(int, input().split())
    p -= 1
    q -= 1
    d = ((L[p][0]-L[q][0])**2 + (L[p][1]-L[q][1])**2)**0.5
    E[p].append((q, d))
    E[q].append((p, d))

def dijkstra(s):
    used = [0]*N
    inf = 10**10
    d = [inf]*N
    h = [(0, s)]
    while h:
        temp = heapq.heappop(h)
        u = temp[1]
        r = temp[0]
        if used[u] == 1:
            continue
        d[u] = r
        used[u] = 1
        for e in E[u]:
            if used[e[0]] == 1:
                continue
            heapq.heappush(h, (r+e[1], e[0]))
    return d[Y-1]

ans = dijkstra(X-1)
print(ans)