백준 [ALGORITHM] - 듣보잡 (1764)

n, m = map(int, input().split())

lst = []
temp = []
ans = dict()

for i in range(n+m):
    lst.append(input())

for i in range(len(lst)):
    if lst[i] in ans:
        ans[lst[i]] += 1
    else:
        ans[lst[i]] = 1

temp = sorted([key for key, value in ans.items() if value != 1])

print(len(temp))
print(*temp,sep='\n')