function modifyAmount( formName, inputName, addValue ) {
  var value = eval('document.'+formName+'.'+inputName).value;
  if( value < 999999 || value > -1 ) {
    value=eval( value+'+('+addValue+')' );
  }
  if( value >= 1 ) {
    eval('document.'+formName+'.'+inputName).value=value;
  }
}