Basic Calculator

This problem requires you to implement a basic calculator that performs simple arithmetic operations. You will be given two numbers and an operator. The operator can be one of the following: + (addition), - (subtraction), * (multiplication), or / (division). The operation is defined mathematically as follows:

\(a \; \text{operator} \; b\)

If the operator is / and b is 0, then the output should be None. If the operator is invalid (i.e. not one of +, -, *, or /), then output exactly Invalid operator.

Note: The result of a valid operation should always be printed as a floating-point number with one decimal point (e.g. 5.0).

inputFormat

The input consists of a single line containing two floating-point numbers and an operator separated by spaces.

For example: 2 + 3

outputFormat

Output the result of the arithmetic operation as a floating-point number with one decimal precision. If a division by zero occurs, output None. If the operator is invalid, output Invalid operator.

## sample

2 + 3

5.0

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