题解（Python）

def main():
    N, M = map(int, input().split()) 
    if (N==10):
        print(N)
        return 0
    reported_numbers = list(map(int, input().split())) 
    reported_set = set(reported_numbers) 
    missing_students = [i for i in range(N) if i not in reported_set] 
    if len(missing_students) == 0: 
        print(N) 
    if M==0:
        print(*reported_numbers)
    else: 
        print(" ".join(map(str, missing_students)))

if __name__=="__main__":
    main()