import sys
input=sys.stdin.readline
from heapq import heappop,heappush
def dijkstra(s,n,edge):
  dist=[float("inf")]*n
  dist[s]=0
  used=[-1]*n
  hq=[[dist[s],s]]
  while hq:
    d,cur=heappop(hq)
    if dist[cur]<d:continue 
    for nx,nxd in edge[cur]:
      if dist[cur]+nxd<dist[nx]:
        dist[nx]=dist[cur]+nxd
        used[nx]=cur
        heappush(hq,[dist[cur]+nxd,nx])
  return dist

n,m=map(int,input().split())
x,y=map(int,input().split())
pq=[tuple(map(int,input().split())) for i in range(n)]
G=[[] for i in range(n)]
for i in range(m):
  p,q=map(int,input().split())
  p-=1
  q-=1
  c=((pq[q][0]-pq[p][0])**2+(pq[q][1]-pq[p][1])**2)**0.5
  G[p].append([q,c])
  G[q].append([p,c])
d=dijkstra(x-1,n,G)
print(d[y-1])