Grandpa was sick. He was hospitalized on April 28 and was not discharged until May 15. How many days did he stay in the hospital?
爷爷生病了，他4月28日住院，直到5月15日才出院，他一共在医院住了多少天．
<gadget id="calculator">3 + 15</gadget>
<output>18</output>

<result>18</result>