Given an arithmetic equation consisting of positive integers, +, -, * and / (no paren­theses), compute the result.

The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.

Example 1:

Input: "3+2*2"

Output: 7

Example 2:

Input: " 3/2 "

Output: 1

Example 3:

Input: " 3+5 / 2 "

Output: 5

Note:

• You may assume that the given expression is always valid.
• Do not use the eval built-in library function.