import sys, heapq as hq

readline = sys.stdin.readline

ns = lambda: readline().rstrip()
ni = lambda: int(readline().rstrip())
nm = lambda: map(int, readline().split())
nl = lambda: list(map(int, readline().split()))

def dijkstra(G, s, t=None):
    """
    G[v] = [(x1, c1), (x2, c2), ...]
    """
    dist = [-1]*len(G)
    dist[s] = 0
    q = [(0, s)]
    while q:
        d, v = hq.heappop(q)
        if d > dist[v]: continue
        for x, c in G[v]:
            if dist[x] < 0 or dist[x] > d + c:
                dist[x] = d + c
                hq.heappush(q, (d + c, x))
    if t is None:
        return dist
    else:
        return dist[t]

def solve():
    n, m = nm()
    X, Y = nm()
    X -= 1; Y -= 1
    points = [tuple(nm()) for _ in range(n)]
    G = [list() for _ in range(n)]
    for _ in range(m):
        u, v = nm()
        u -= 1; v -= 1
        p, q = points[u]
        r, s = points[v]
        c = ((p - r)**2 + (q - s)**2) ** .5
        G[u].append((v, c))
        G[v].append((u, c))
    print(dijkstra(G, X, Y))
    return

solve()