This is about is typically computed from other input. There is an entry right above  14f where you can enter and adjustment.

The program automatically uses the entries from investment income you entered in boxes 1 - 8.  You normally don't need to deal with entering 14E.

If your box 14E entry is different from those amounts, there is a box towards the bottom of the Box 14 - Other Information section Other investment income - Form 4952 that will adjust the amount.  

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