Determine Least Significant Digits

[C# Programming]

Hi Guys. I need to know how to determine the least significan't digits from a number. Now, I'm calculating a bunch of numbers and the total comes to say 17 digits in total. I need to only use ythe last significant 12 digits from the 13 digits. HOw do I determine what the least significant digits are?

As an example:
The calulated value is: 865807311427710

From this number I want to only obtain 807311427710.

The problem I am having is that the calculated value can be any amount of digits long.

Any help will be greatly appreciated.

Thanks

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