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

input = sys.stdin.buffer.readline


def main():

    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
    dist[x] = 0
    while edgelist:
        nowd, nowedge = heappop(edgelist)
        if nowedge == y:
            print(nowd)
            exit()
        if dist[nowedge] < nowd:
            continue
        for delta, nextedge in graph[nowedge]:
            if dist[nextedge] < delta + nowd:
                continue
            dist[nextedge] = delta + nowd
            heappush(edgelist, (nowd + delta, nextedge))

    print("error")
    exit()


if __name__ == "__main__":
    main()