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)