import random as s
def p(q,k=50):
 d=(q-1)>>1
 while d&1==0:d>>=1
 while k:
  k-=1
  t=d
  y=pow(s.randint(1,q-1),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 0
 return 1

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 p(i-8):print(14)
else:print(8)