import random as s
def p(q,k=1000):
 if q%2==0:return 0
 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

n=int(input())
if p(n):
 print(n)
elif p(n//2):
 print(n//2)
else:
  for i in range(3,n+3):
   if n%i==0:
    print(i)
    break
  else:print(n)