input()

C = sorted(list(map(int, input().split())))

C_MAX = len(C)

input()

W = sorted(list(map(int, input().split())))

W_MAX = len(W)

is_processed = [False for _ in range(W_MAX)]

W_index, C_index = 0, 0

result = 1

while False in is_processed:

if W[W_index] > C[-1]:

result = -1

break

elif is_processed[W_index]:

W_index += 1

continue

elif C_index == C_MAX:

C_index = 0

result += 1

if W[W_index] >= C[C_index]:

for j in range(C_index, C_MAX):

if W[W_index] <= C[j]:

C_index = j

is_processed[W_index] = True

break

elif W[W_index] < C[C_index]:

for j in range(W_MAX - 1, W_index - 1, -1):

if not is_processed[j] and W[j] <= C[C_index]:

is_processed[j] = True

break

C_index += 1

print(result)