import java.io.*;

class Main{
  public static void main(String[] args)throws IOException {

    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    int n=Integer.parseInt(br.readLine());
    int sum=0;

    if(n%2==0){
      sum=(n/2)*(n+1);
    }else{
      sum=((n+1)/2)+(n+1)*(n-1)/2;
    }

    System.out.println(sum);
  }
}