from scipy.sparse.csgraph import connected_components
from scipy.sparse import csr_matrix

N, M, S, T = map(int, input().split())
S -= 1
T -= 1
P = tuple(map(int, input().split()))
frm, to = [0] * M, [0] * M
for i in range(M):
    a, b = (int(x) - 1 for x in input().split())
    frm[i] = a
    to[i] = b

matr = csr_matrix(([1] * M, (frm, to)), shape=(N, N))
p, labels = connected_components(matr)

ls, ps = labels[S], P[S]
st = set()
for x, p in zip(labels, P):
    if x == ls and p < ps:
        st.add(p)
print(len(st))