from math import sqrt
from heapq import heappush, heappop
import sys

input = sys.stdin.buffer.readline

n, m = map(int, input().split())
x, y = map(int, input().split())
x -= 1
y -= 1


def kyori(a, b, c, d):
    return sqrt((a - c) ** 2 + (b - d) ** 2)


XY = [list(map(int, input().split())) for _ in range(n)]
graph = [[] for _ in range(n)]
for _ in range(m):
    p, q = map(int, input().split())
    a, b = XY[p - 1]
    c, d = XY[q - 1]
    temp = kyori(a, b, c, d)
    graph[p - 1].append((temp, q - 1))
    graph[q - 1].append((temp, p - 1))


edgelist = [(0, x)]
dist = [10 ** 10] * n
used = [False] * n
while edgelist:
    nowd, nowedge = heappop(edgelist)
    if used[nowedge]:
        continue
    if nowedge == y:
        print(nowd)
        exit()
    used[nowedge] = True
    dist[nowedge] = nowd
    for delta, nextedge in graph[nowedge]:
        if used[nextedge]:
            continue
        heappush(edgelist, (nowd + delta, nextedge))

print("error")
exit()