single textbox value spliting into multiple textbox

<script>
    window.update = function () {
    var one = document.getElementById('one'),
    two = document.getElementById('two');
    three = document.getElementById('three');
    four = document.getElementById('four');
    five = document.getElementById('five');
    six = document.getElementById('six');

    //checking if value is less than 100
    if(one.value < 50) {
        two.value = 0;
        three.value = 0;
        four.value = 0;
    five.value = 0;
        six.value = one.value;  
    }
    else if(one.value == 50) {
        two.value = 0;
        three.value = 50;   
        four.value = 0;
  		five.value = 0;
        six.value = 0;
    }
    else if (one.value < 100) {
        two.value = 0;
        three.value = 50;    
        four.value = 0;
		five.value = 0;
        six.value = parseInt(one.value) - three.value;     
    } else if (one.value == 100) {
        two.value = one.value;    
        three.value = 0;
        four.value = 0;
		five.value = 0;
        six.value = 0;
    } else if (one.value > 100)
	{
        two.value = 100;
        if ((one.value - two.value) >= 50) 
		{
            three.value = 50;
            if ((one.value - two.value - three.value) >= 50) four.value = 50; 
        else 
			four.value = 0;
			            if ((one.value - two.value - three.value - four.value) 
    >= 60) five.value = 60;
						else
						five.value = 0;

            six.value = one.value - two.value - three.value - four.value - five.value;
        } 
		else 
		{
            three.value = 0;
            four.value = 0;
			five.value = 0;
            six.value = one.value - two.value - three.value - four.value - five.value;
        }
    }
    }
    </script>
  <br>
    <p align="center">Enter the amount to be paid
    <input id="one" type="text" onchange="update();" onkeypress="update()" />
    <br>fees1
    <input id="two" type="text" name="txt" onchange="checknumber(this)" />100
    <br>fees2
    <input id="three" type="text" />50
    <br>fees3
    <input id="four" type="text" />50
    <br>fees4
    <input id="five" type="text" />60
    <br>balance fees
    <input id="six" type="text" />
    <br></br></br></br></br></br></br></p></br>