import sys

from scipy.sparse import coo_matrix
from scipy.sparse.csgraph import shortest_path


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 = []
    apnd = dis.append
    for i, j in zip(P, Q):
        apnd((p[j - 1] - p[i - 1]) ** 2 + (q[j - 1] - q[i - 1]) ** 2)
    coo = coo_matrix((dis, (P, Q)), (N + 1, N + 1))
    csr = coo.tocsr()
    ans = shortest_path(csr, indices=X, directed=False)
    print(ans[Y] ** 0.5)


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

main()