from scipy.sparse import csr_matrix
from scipy.sparse.csgraph import dijkstra
from sys import stdin


def main():
    input = lambda: stdin.readline()[:-1]
    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) ** 0.5)
    csr = csr_matrix((dis, (P, Q)), (N + 1, N + 1))
    ans = dijkstra(csr, indices=X, directed=False)
    print(ans[Y])


main()