n = int(input())
l, r = zip(*[map(int, input().split()) for i in range(n)])
p = int(input())
x = list(map(int, input().split()))
l = list(l)
r = list(r)
from bisect import bisect_left as bl
X = set(x)
last = 2

rest = []
for i in range(n):
    cnt = bl(x, r[i] + 1) - bl(x, l[i])
    if cnt > 2:
        print("impossible")
        exit()
    rest.append(2 - cnt)

i = 0
ans = []
while i < n:
    if rest[i] == 0:
        i += 1
        continue
    j = i
    while j + 1 < n and r[j] == l[j+1] and rest[j+1] and (not r[j] in X):
        j += 1
    
    for k in range(i, j):
        if rest[k] and rest[k+1]:
            ans.append(r[k])
            rest[k] -= 1
            rest[k+1] -= 1
    i = j + 1

for i in range(n):
    j = l[i] + 1
    while rest[i]:
        if not j in X:
            ans.append(j)
            rest[i] -= 1

print(len(ans))
print(*ans)