The basics

Create function calc which gets operator and two numbers and returns the calculation result.

Examples:

calc('+', 1, 3)  ->  4

calc('*', 2, 3)  ->  6

calc('/', 1, 4) - >  0.25

calc('-', 1, 3)  ->  -2

for now deal only with the basic operators - +, -, *, / 

The return value can be float and not only int!