import java.io.*;
import java.util.*;
class gambling 
{
  public static void main( String[] args ) throws IOException
  {
    while( true )
    {
      BufferedReader bf = new BufferedReader( new InputStreamReader( System.in ) );

      String line = bf.readLine();

      if ( line.equals( "0" ) )
      {
        break;
      }
      StringTokenizer st = new StringTokenizer( line, " " );
      int number_int = st.countTokens();
      if ( number_int > 1 )
      { 
        continue;
      }

      int delka = Integer.parseInt( line );
      int k = ( int ) ( ( double ) (delka - 1) ) / 2;
      
      int a = ( int ) Math.floor( (double ) delka / k );

      int b = delka - ( k * a );

      int c = k - b;

      long tmp1 = ( ( 1 + delka ) * delka ) / 2;
      long tmp2 = ( ( 1 + c ) * c ) / 2;
      System.out.printf( "%d\n", tmp2 + tmp1 );
    }
  }

}