Complete the function, which calculates how much you need to tip based on the total amount of the bill and the service. 
You need to consider the following ratings:
- Terrible: tip 0%
- Poor: tip 5%
- Good: tip 10%
- Great: tip 15%
- Excellent: tip 20%
The rating is **case insensitive** (so "great" = "GREAT"). If an unrecognised rating is received, then you need to return:
* `"Rating not recognised"` in Javascript, Python and Ruby...
* ...or `null` in Java
* ...or `-1` in C#
Because you're a nice person, you **always round up** the tip, regardless of the service.
from math import ceil

d = {
    "terrible":0, "poor":5, "good":10, "great":15, "excellent":20    
}

def calculate_tip(amount, rating):
    #your code here
    rating = rating.lower()
    if rating not in d.keys():
        return 'Rating not recognised'
    else:
        return ceil(amount*d[rating]/100)
from math import ceil

d = {
    "terrible":0, "poor":5, "good":10, "great":15, "excellent":20    
}

def calculate_tip(amount, rating):
    #your code here
    rating = rating.lower()
    if rating not in d.keys():
        return 'Rating not recognised'
    else:
        return ceil(amount*d[rating]/100)