import random
def is_prime3(q,k=50):
 q=abs(q)
 if q==2:return True
 if q<2 or q&1 == 0:return False
 d=(q-1)>>1
 while d&1==0:d>>=1
 for i in range(k):
  a=random.randint(1,q-1)
  t=d
  y=pow(a,t,q)
  while t!=q-1 and y!=1 and y!=q-1: 
   y=pow(y,2,q)
   t<<=1
  if y!=q-1 and t&1==0:
   return False
 return True

i=int(input())
if i==4:print(3)
elif i==6:print(5)
elif i==8 or i==9 or i== 10 or i==15 or i==16 or i==22:print(7)
elif i==12:print(11)
elif i==14:print(13)
elif i==20 or i==21:print(19)
elif i==24 or i==25:print(23)
elif (i - 1) % 8 == 0 and is_prime3(i - 8):print(14)
else:print(8)