import sys
readline = sys.stdin.readline
from math import *
from heapq import heappush, heappop
inf = float('inf')


def naive_dijkstra(s, g, N):
    # ゴールがない場合はg=-1とする。

    dist = [inf] * N
    mindist = [inf] * N
    seen = [False] * N
    Q = [(0, s)]
    while Q:
        c, m = heappop(Q)
        if seen[m]:
            continue
        seen[m] = True
        dist[m] = c
        if m == g:
            return dist

        #------heapをアップデートする。--------
        for u, C in G[m]:
            if seen[u]:
                continue
            newdist = dist[m] + C

            #------------------------------------
            if newdist >= mindist[u]:
                continue
            mindist[u] = newdist
            heappush(Q, (newdist, u))
    return dist

def dist(i, j):
    return sqrt((P[i] - P[j]) ** 2 + (Q[i] - Q[j]) ** 2)

N, M = map(int, readline().split())
X, Y = map(int, readline().split())
X, Y = X - 1, Y - 1
P, Q = [0] * N, [0] * N
for i in range(N):
    P[i], Q[i] = map(int, readline().split())
    
G = [[] for i in range(N)]
for i in range(M):
    p, q = map(int, readline().split())
    p, q = p - 1, q - 1
    G[p].append((q, dist(p, q)))
    G[q].append((p, dist(p, q)))
    
D = naive_dijkstra(X, Y, N)
print(D[Y])