require 'prime'
n=gets.to_i
c=Prime.prime_division(n)
c.each{|e|
    if e[0]==2
        if n==3||c.include?(3)
            p 3;exit
        elsif e[1]>1
            p 4;exit
        end
        next
    end
    p e[0]
    exit
}
p n