function updateTotalamount()
{
	cost = document.getElementById('creditspurchase_cost').value;
	credits = document.getElementById('creditspurchase_credits').value;
	
	document.getElementById('creditspurchase_totalamount').value = credits * cost;
	
	document.getElementById('hidden_creditspurchase_cost').value = cost;
	document.getElementById('hidden_creditspurchase_credits').value = credits;
	document.getElementById('hidden_creditspurchase_totalamount').value = credits * cost;
}