import sys
sys.setrecursionlimit(10000000)
MOD = 10 ** 9 + 7
INF = 10 ** 15
from heapq import heapify,heappop,heappush

def dijkstra(G,s = 0): #sを始点とした最短経を求める
    n = len(G)
    dist = [INF] * n
    dist[s] = 0
    q = [(0,s)]
    while q:
        d,v = heappop(q)
        if dist[v] < d:
            continue
        for e,cost in G[v]:
            if dist[e] > dist[v] + cost:
                dist[e] = dist[v] + cost
                heappush(q,(dist[e],e))
    return dist
N,M = map(int,input().split())
X,Y = map(int,input().split())
point = [list(map(int,input().split())) for _ in range(N)]
dist = lambda i,j:((point[i][0] - point[j][0])*(point[i][0] - point[j][0]) + (point[i][1] - point[j][1])*(point[i][1] - point[j][1]))**0.5
G = [[] for _ in range(N)]
for _ in range(M):
    x,y = map(int,input().split())
    x -= 1
    y -= 1
    d = dist(x,y)
    G[x].append((y,d))
    G[y].append((x,d))
dist = dijkstra(G,X - 1)
ans = dist[Y - 1]
print(ans)