In this kata you need to write a function that will receive two strings (```n1``` and ```n2```), each representing an integer as a binary number. A third parameter will be provided (```o```) as a string representing one of the following operators: add, subtract, multiply.
Your task is to write the calculate function so that it will perform the arithmetic and the result returned should be a string representing the binary result.
Examples:
```
1 + 1 === 10
10 + 10 === 100
```
Negative binary numbers are usually preceded by several 1's. For this kata, negative numbers can be represented with the negative symbol at the beginning of the string.
Examples of negatives:
```
1 - 10 === -1
10 - 100 === -10
```
def calculate(n1, n2, o):
    ops = {
        "add": (lambda a, b: a + b), 
        "subtract": (lambda a, b: a - b), 
        "multiply": (lambda a, b: a * b)}
    n = ops[o](int(n1, 2), int(n2, 2))
    s = str(bin(n))
    return  "-" + s[3:] if n < 0 else s[2:]
def calculate(n1, n2, o):
    ops = {
        "add": (lambda a, b: a + b), 
        "subtract": (lambda a, b: a - b), 
        "multiply": (lambda a, b: a * b)}
    n = ops[o](int(n1, 2), int(n2, 2))
    s = str(bin(n))
    return  "-" + s[3:] if n < 0 else s[2:]