规则1：实现 +、-、X、/ 四则运算，数据仅包含整数，不考虑计算结果溢出的情况

规则2：程序仅需要实现类似"a + b * c / d - e" 这种类型字符串的计算，式子中操作符的个数不超过10个。其他复杂情况不考虑。

例子1：

输入： 1 + 2

输出： 3

输入： 1 + 2 * 3 - 4 / 2

输出： 5-Rule 1: realize+,-X,/arithmetic, data contain only integer, don t consider the calculation results of the spill

Rule 2: program only need to implement similar "a+ b* c/d-e" this type of string calculation, the number of operators in the mean no more than 10. Other complex condition is not considered.

Example 1:

Input: 1+ 2

Output: 3

Input: 1+ 2* 3-4/2

Output: 5