n = int(input('輸入一個數字:'))
def getNumber(n):
	if n <= 3:
		if n > 1:
			return n
		else:
			return False
	else:
		ls = [];
		for i in range(3,n,2):
			z = check(i)
			if z :
				ls.append(i)
		return max(ls)
#檢查是否是質數
def check(n):
	if n > 1:
		for i in range(2,n):
			#print(i)
			if( n % i ) == 0:
				#print('不是')
				return False
				break
		else:
			return True
	else:
		return False
bgnum = getNumber(n)
if bgnum:
	print('%s是不大於%s的最大質數'%(bgnum,n))
else:
	print('請輸入大於1的數')