How many active volcanoes are there on earth? Please calculate a three-digit number, its tens digit is 3 greater than the hundreds digit, and the ones digit is 4 less than the tens digit, half of the sum of its digits is exactly equal to the tens digit. When you figure out this three-digit number, you know the number of active volcanoes.
地球上有多少座活火山？请你算出一个三位数，它的十位数比百位数大3，个位数比十位数少4，它的各位数字之和的一半恰好等于十位数．当你算出这个三位数，就知道了活火山的数目．
<result>437</result>