amcharts Column and line mix

HTML

<script src="http://www.amcharts.com/lib/amcharts.js" type="text/javascript"></script>
<div id="chartdiv" style="width: 100%; height: 362px;"></div>

JavaScript

var chart;
var chartData = [{
    year: 2005,
    income: 23.5,
    expenses: 18.1},
{
    year: 2006,
    income: 26.2,
    expenses: 22.8},
{
    year: 2007,
    income: 30.1,
    expenses: 23.9},
{
    year: 2008,
    income: 29.5,
    expenses: 25.1},
{
    year: 2009,
    income: 24.6,
    expenses: 25.0}];


AmCharts.ready(function() {
    // SERIAL CHART  
    chart = new AmCharts.AmSerialChart();
    chart.pathToImages = "http://www.amcharts.com/lib/images/";
    chart.autoMarginOffset = 0;
    chart.marginRight = 0;
    chart.dataProvider = chartData;
    chart.categoryField = "year";
    chart.startDuration = 1;

    // AXES
    // category
    var categoryAxis = chart.categoryAxis;
    categoryAxis.gridPosition = "start";

    // value
    // in case you don't want to change default settings of value axis,
    // you don't need to create it, as one value axis is created automatically.
    // GRAPHS
    // column graph
    var graph1 = new AmCharts.AmGraph();
    graph1.type = "column";
    graph1.lineColor = "#5475d3";
    graph1.title = "Income";
    graph1.valueField = "income";
    graph1.lineAlpha = 0;
    graph1.fillAlphas = 0.85;
    chart.addGraph(graph1);

    // line
    var graph2 = new AmCharts.AmGraph();
    graph2.type = "line";
    graph2.title = "Expenses";
    graph2.valueField = "expenses";
    graph2.lineThickness = 2;
    // graph2.bullet = "round";
    chart.addGraph(graph2);

    // LEGEND                
    var legend = new AmCharts.AmLegend();
    chart.addLegend(legend);

    // WRITE
    chart.write("chartdiv");
});