using System;
public class Program
{
public static void Main()
int i,k=0,n,j;
n=Convert.ToInt32(Console.ReadLine());
for(i=1;i<=n;i++)
k=0;
for(j=1;j<=i;j++)
if(i%j==0)
k++;
}
if (k==2)
Console.WriteLine(i);