while True: try: num = int(input()) count = 0 if num > 4: for i in range(2,num): #用num//2可以减少回圈次数 if num % i == 0: count += 1 if count == 1: print('no') break if count == 0: print('yes') elif num == 2&nbs***bsp;num == 3: print('yes') else: print('no') except: break