import sys
from math import sqrt
from heapq import heappush, heappop
INF = 10**10
input = sys.stdin.readline
def main():
    N, M = map(int,input().split())
    X, Y = map(int,input().split())
    X -= 1
    Y -= 1
    D = []
    for _ in range(N):
        D.append(list(map(int,input().split())))
    K = [[] for _ in range(N)]
    for _ in range(M):
        P, Q = map(int,input().split())
        P -= 1
        Q -= 1
        K[P].append((Q,sqrt((D[P][0]-D[Q][0])**2+(D[P][1]-D[Q][1])**2)))
        K[Q].append((P,sqrt((D[P][0]-D[Q][0])**2+(D[P][1]-D[Q][1])**2)))
    dist = [INF] * N
    def dijkstra(N, G, s):
        que = [(0, s)]
        dist[s] = 0
        while que:
            c, v = heappop(que)
            if dist[v] < c:
                continue
            for t, cost in G[v]:
                if dist[v] + cost < dist[t]:
                    dist[t] = dist[v] + cost
                    heappush(que, (dist[t], t))
    dijkstra(N, K, X)
    print(dist[Y])
if __name__ == '__main__':
    main()