import sys
from math import sqrt
input = sys.stdin.readline
N, M = map(int, input().split())
X, Y = map(int, input().split())
e = [[] for _ in range(N + 1)]
ps = [(0, 0)]
for _ in range(N):
  p, q = map(int, input().split())
  ps.append((p, q))
for _ in range(M):
  p, q = map(int, input().split())
  e[p].append((q, sqrt((ps[p][0] - ps[q][0]) ** 2 + (ps[p][1] - ps[q][1]) ** 2)))
  e[q].append((p, sqrt((ps[p][0] - ps[q][0]) ** 2 + (ps[p][1] - ps[q][1]) ** 2)))
import heapq
hpush = heapq.heappush
hpop = heapq.heappop
class dijkstra:
  def __init__(self, n, e):
    self.e = e
    self.n = n
  def path(self, s):
    d = [float("inf")] * (self.n + 1)
    vis = [0] * (self.n + 1)
    d[s] = 0
    h = [(0, s)]
    while len(h):
      v0, v1 = hpop(h)
      if vis[v1]: continue
      vis[v1] = 1
      for p in self.e[v1]:
        d[p[0]] = min(d[p[0]], d[v1] + p[1])
        if vis[p[0]]: continue
        hpush(h, (d[p[0]], p[0]))
    return d
dij = dijkstra(N, e)
print(dij.path(X)[Y])