If I multiply $$333333333333333$$ by $$777777777777777$$ and add the first and last digits of the product, the sum is． 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Calculation of Multi-digit Numbers
Just as for $$3\times7$$, $$33\times77$$, and $$333\times777$$, the first digit is a $$2$$, the last digit is a $$1$$, and the sum is $$2+1=3$$. 