\begin{verbatim}
  counter = 0;
  for( i=1; i<=20; i++ )
     for( j=1; j<=20; j++ )
        for( k=1; k<=20; k++ )
           counter = counter + 1;
\end{verbatim}

\bigskip

\begin{verbatim}
  counter = 0;
  for( i=1; i<=20; i++ )
     for( j=i; j<=20; j++ )
        for( k=j; k<=20; k++ )
           counter = counter + 1;
\end{verbatim}
