calculate the result based on the given expression. The instruction contains numbers followed by operators e.g. "1+2-4*2+1/2*2". Return the result of the given string as an int (acceptable operators are + - * /). You need to parse the operations from left to right (rather than following standard order of operators in which some operators have priority over others). You can always assume there are at least one digit number and one operator inside the given string. The given string always starts with a digit and its length is always greater than 1. You can always assume all numbers are single-digit integers, and