from collections import defaultdict
from math import sqrt
from heapq import heapify, heappop, heappush

n, m = map(int, input().split())
x, y = map(int, input().split())
x -= 1
y -= 1
P = [list(map(int, input().split())) for _ in range(n)]
Edge = defaultdict(list)
for _ in range(m):
    p, q = map(int, input().split())
    p -= 1
    q -= 1
    d = sqrt((P[p][0] - P[q][0])**2 + (P[p][1] - P[q][1])**2)
    Edge[p].append((q, d))
    Edge[q].append((p, d))

INF = 10**18
D = [INF for _ in range(n)]
D[x] = 0
H = [(0, x)]
heapify(H)
while H:
    d, cp = heappop(H)
    if cp == y:
        print(d)
        break
    if d > D[cp]:
        continue
    for np, dd in Edge[cp]:
        if d + dd >= D[np]:
            continue
        D[np] = d + dd
        heappush(H, (d + dd, np))