class Integer
    def prime?
      n = self.abs()
      return true if n == 2
      return false if n == 1 || n & 1 == 0
      d = n-1
      d >>= 1 while d & 1 == 0
      20.times do 
        a = rand(n-2) + 1
        t = d
        y = ModMath.pow(a,t,n)
        while t != n-1 && y != 1 && y != n-1
          y = (y * y) % n
          t <<= 1
        end
        return false if y != n-1 && t & 1 == 0
      end
      return true
    end
  end
  
  module ModMath
    def ModMath.pow(base, power, mod)
      result = 1
      while power > 0
        result = (result * base) % mod if power & 1 == 1
        base = (base * base) % mod
        power >>= 1;
      end
      result
    end
  end
n = gets.to_i
a = [4, 6, 8, 9, 10, 15, 16, 22, 12, 14, 20, 21, 24]
b = [3, 5, 7, 7,  7,  7,  7,  7, 11, 13, 19, 19, 23]
a.length.times do |i|
    if a[i] == n
        puts b[i]
        exit
    end
end
if !(n - 8).prime?
    puts 8
else
    puts 14
end