from math import sqrt
import heapq

def dijkstra(s, h, graph):
    n = len(graph)-1
    dist = [float("inf") for i in range(n+1)]
    dist[s] = 0
    pq = []
    heapq.heapify(pq)
    heapq.heappush(pq, (0, s))
    while pq:
        mini_dis, node = heapq.heappop(pq)
        if dist[node] < mini_dis:
            continue
        for w, point in graph[node]:
            if dist[point] < w:
                continue
            newlen = dist[node]+w
            if newlen < dist[point]:
                heapq.heappush(pq, (newlen, point))
                dist[point] = newlen
    return dist

N,M = map(int,input().split())
X,Y = map(int,input().split())
l = [[] for _ in range(N+1)] 
d =  [[] for _ in range(N+1)] 
for i in range(1,N+1):
  a,b = map(int,input().split())
  d[i].append(a)
  d[i].append(b)

for _ in range(M):
  a,b = map(int,input().split())
  dist = sqrt((d[a][0]-d[b][0])**2 + (d[a][1]-d[b][1])**2)
  l[a].append((dist,b))
  l[b].append((dist,a))
  
ans = dijkstra(X, Y, l)

print(ans[Y])