import sys
from math import sqrt

from scipy.sparse import coo_matrix
from scipy.sparse.csgraph import dijkstra


def input():
    return sys.stdin.readline()[:-1]


def main():
    N, M = map(int, input().split())
    X, Y = map(int, input().split())
    p, q = zip(*[map(int, input().split()) for _ in [0] * N])
    P, Q = zip(*[map(int, input().split()) for _ in [0] * M])

    dis = [sqrt((p[j - 1] - p[i - 1]) ** 2 + (q[j - 1] - q[i - 1]) ** 2) for i, j in zip(P, Q)]
    csr = coo_matrix((dis, (P, Q)), (N + 1, N + 1)).tocsr()
    ans = dijkstra(csr, indices=X, directed=False)
    print(ans[Y])


if not __debug__:
    f = open(sys.argv[1], "r")
    sys.stdin = f

main()