main.py

N, M = map(int, input().split())

all_names = set()
name1 = set()
name2 = set()

for _ in range(N):
    name = input()
    name1.add(name)
    all_names.add(name)

answer = []

for _ in range(M):
    name = input()
    name2.add(name)
    all_names.add(name)

for name in all_names:
    if name in name1 and name in name2:
        answer.append(name)

answer.sort()

print(len(answer))
for name in answer:
    print(name)