import sys
input=sys.stdin.readline

import heapq

INF=2<<28

def dijkstra(G,start,n):#グラフ,初期頂点,頂点数

    dist=[INF]*n;dist[start]=0
    used=[False]*n;used[start]=True
    q=[]

    for v in G[start]:
        heapq.heappush(q,v)
    
    while len(q)>0:
        now=heapq.heappop(q)
        if used[now[1]]:
            continue
        v=now[1]
        dist[v]=now[0]
        used[v]=True

        for e in G[v]:
            if not used[e[1]]:
                heapq.heappush(q,(e[0]+dist[v],e[1]))

    return dist
def main():
    n,m=map(int,input().split())
    x,y=map(int,input().split())
    x,y=x-1,y-1
    l=[tuple(int(i) for i in input().split()) for _ in range(n)]
    g=[[] for _ in range(n)]
    for _ in range(m):
        p,q=map(int,input().split())
        p,q=p-1,q-1
        dis=((l[q][0]-l[p][0])**2+(l[q][1]-l[p][1])**2)**0.5
        g[p].append((dis,q))
        g[q].append((dis,p))
    a=dijkstra(g,x,n)
    print(a[y])

if __name__=="__main__":
    main()