4 identical bottles are respectively filled with a certain amount of oil, and each bottle is weighed together with other bottles respectively, and the resulting weight in kilograms is as follows: 8, 9, 10, 11, 12, 13. It is known that the sum of the weights of the four empty bottles and the sum of the masses of the oil are prime numbers. So how many kilograms of oil are there in the two heaviest bottles?
4只同样的瓶子分别装有一定数量的油，每瓶和其它各瓶分别合称一次，所得重量的千克数如下：8，9，10，11，12，13．已知这四只空瓶的重量之和以及油的质量之和都为质数．那么最重的两瓶内共有油多少千克？
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 2</gadget>
<output>1</output>

<gadget id="calculator">13 - 1</gadget>
<output>12</output>

<result>12</result>