She's up all night 'til the sun. I'm up all night to get SUM

Do you remember Sigma from math class? The summation symbol!

Don't worry if the sight of this is scary to you. It's actually a lot easier than it looks. The simple ideas is that if I ask you for Sigma-4 you add up all the numbers from 1 to 4.

Write a Python function that conforms to the following:

• Function name
• summation()
• Parameters
• a non-negative integer
• Return value
• The summation of all of the integers from 1 to the input parameter
• Examples
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