/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
	    Scanner sc=new Scanner(System.in);
	    int n=sc.nextInt();
	    int f=0;
	    int s=1;
	    int sum=f+s;
	    int i=3;
	    if(n==1){
	    	System.out.println("0");
	    }
	    if(n==2){
	    	System.out.println("1");
	    }
	    while(i<=n){
	    	sum+=i;
	    	f=s;
	    	s=sum;
	    	i++;
	    }
	    System.out.println(sum);
	    }
	    
}