简单的计算器

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。

例如

输入： 1 + 2 * 3 - 4 / 2

输出： 5-A simple calculator



Rule 1: achieve+,-, X, \/four operations, the data contains only integers, not considering the calculation results of an overflow condition



Rule 2: program is needed to achieve similar " a+ b* C/D- e " this type string calculation formula of operator, the number does not exceed 10. Other complex situation is not considered.



For example



Input: 1+ 2* 3- 4/2



Output: 5