r =10000001
p = [1]*r
p[0]= p[1] = 0
for i in range(int(r**0.5)):
	if p[i]:
		p[2*i::i] = [0 for j in range(2*i,r,i)]
		
while 1:
	try:
		n = input()
		if n == 0: break
		n -= 1-n%2
		while any(not p[n-i] for i in [0,2,6,8]):
			n -= 2
		print n
	except:
		pass