source_code: import java.util.*;
  import java.io.*;
  public class A{
         
         public static void main(String args[]){
                Scanner sc = new Scanner(System.in);
                int n = sc.nextInt();
                int ans = 0;
                for(int i = 1; i <= n; i++){
                       ans += ((i*2) <= n) ? i : n-i+1;
                }
                System.out.println(ans);
         }
  }