//Ëæ»úÊý²úÉúÆ÷
function rand(r)
{
    var seed = Math.random();
    return Math.ceil(seed * r);
}

function showad(n)
{
    document.write(code[n]);
}

var sumRate = 25;
var count = 5;
var rate = new Array(count);
var code = new Array(count);

rate[0] = 5;
rate[1] = 5;
rate[2] = 5;
rate[3] = 5;
rate[4] = 5;

code[0] = '<scr' + 'ipt src="http://online4.lianmeng.com/cn/12/89013_112431.php"></scr' + 'ipt>';
code[1] = '<scr' + 'ipt src="http://online4.lianmeng.com/cn/12/121865_150533.php"></scr' + 'ipt>';
code[2] = '<scr' + 'ipt src="http://online4.lianmeng.com/cn/12/121865_150536.php"></scr' + 'ipt>';
code[3] = '<scr' + 'ipt src="http://online4.lianmeng.com/cn/12/121864_150534.php"></scr' + 'ipt>';
code[4] = '<scr' + 'ipt src="http://online4.lianmeng.com/cn/12/121864_150535.php"></scr' + 'ipt>';


var randnum = rand ( sumRate ); 

var begin = 1;
var end = 1;
var i = 0;
while(i<count)
{
    begin = end;
    end += rate[i];
    if(randnum >= begin && randnum < end){
        showad(i);
        break;
    }
    i++;
}