An arithmetic expression is written as a string, for example: "10 + 25 - 12" or "10 + 25 - 12 + 20 - 1 + 3", etc. That is, the number of actions can be different. It is necessary to perform the calculation and display the result on the screen. It is assumed that only addition (+) and subtraction (-) are used here as arithmetic operations, and non-negative integers are used as operands. Note that these operators can be written with or without spaces.

def arithmetic(expr):
    # replace all spaces
    expr = expr.replace(" ", "")
    # split at operators
    expr_arr = re.split('\+|-', expr)
    print(expr_arr)
    # iterate
    for num, op in zip(expr_arr[1:], expr_arr[:-1]):
        if op == "-":
            expr_arr[0] = str(int(expr_arr[0]) - int(num))
        else:
            expr_arr[0] = str(int(expr_arr[0]) + int(num))
    
    return expr_arr[0]
    
arithmetic("10+25-12")