import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
from heapq import heappop, heappush
INF = float('inf')

def getlist():
	return list(map(int, input().split()))

class Graph(object):
	def __init__(self):
		self.graph = defaultdict(list)

	def __len__(self):
		return len(self.graph)

	def add_edge(self, a, b, w):
		self.graph[a].append((b, w))

class Dijkstra(object):
	def __init__(self, graph, s):
		self.g = graph.graph
		self.dist = defaultdict(lambda: INF); self.dist[s] = 0
		self.Q = []
		heappush(self.Q, (self.dist[s], s))
		while self.Q:
			dist_u, u = heappop(self.Q)
			if self.dist[u] < dist_u:
				continue
			for v, w in self.g[u]:
				alt = dist_u + w
				if self.dist[v] > alt:
					self.dist[v] = alt
					heappush(self.Q, (alt, v))

#処理内容
def main():
	N, M = getlist()
	X, Y = getlist()
	X -= 1; Y -= 1
	node = []
	for i in range(N):
		p, q = getlist()
		node.append([p, q])

	G = Graph()
	for i in range(M):
		P, Q = getlist()
		P -= 1; Q -= 1
		x1, y1 = node[P]
		x2, y2 = node[Q]
		dist = ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
		G.add_edge(P, Q, dist)
		G.add_edge(Q, P, dist)

	D = Dijkstra(G, X)
	ans = D.dist[Y]
	print(ans)

if __name__ == '__main__':
	main()