JSTL cannot parse a double variable multiplied by an integer variable?

If I set two variables in my controller:

double doubleAmount = 18.0;
int integerAmount = 2;

And then try to multiply them in my JSTL code:

<c:set var="result" value="${doubleAmount} * ${integerAmount}"/>

I get this error:

javax.servlet.Serv开发者_开发技巧letException: 
javax.servlet.jsp.JspException: 
In <formatNumber>, 
value attribute can not be parsed into java.lang.Number: 
"18.0 * 2"

How do I perform this operation in my JSTL code?

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Try <c:set var="result" value="${doubleAmount * integerAmount}"/> please.