from heapq import heappush, heappop
import math
INF = float('inf')

N, M = map(int, input().split())
X, Y = map(int, input().split())
p = [list(map(int, input().split())) for _ in range(N)]
adj = [[] for _ in range(N)]
for i in range(M):
    P, Q = map(int, input().split())
    x1, y1 = p[P-1]
    x2, y2 = p[Q-1]
    adj[P-1].append((Q-1, math.sqrt((x1-x2)**2+(y1-y2)**2)))
    adj[Q-1].append((P-1, math.sqrt((x1-x2)**2+(y1-y2)**2)))

def dijkstra(s, n):
    dist = [INF] * n
    hq = [(0, s)]
    dist[s] = 0
    seen = [False] * n
    while hq:
        v = heappop(hq)[1]
        seen[v] = True
        for to, cost in adj[v]:
            if seen[to] == False and dist[v] + cost < dist[to]:
                dist[to] = dist[v] + cost
                heappush(hq, (dist[to], to))
    return dist
d = dijkstra(X-1, N)
print(d[Y-1])