import java.util.Scanner;
public class Exercise1_3 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n=sc.nextInt();
int sum=0;
//Use for or while loop do the operation.
int result=1;
int i=0;
while(result<=n)
{
if(i%2==0)
{
if(i%3==0)
{
sum=sum+i;
}
result=result+1;
}
i=i+1;
}
System.out.print(sum);
}
}