ScicomLoveBug

There are initially $N$ lovebugs, and the number increases by $A$ each day. Therefore, during $D$ days, the number of additional lovebugs is $A \times D$.

The answer is $N + A \times D$. This value can exceed the range of a $32$-bit integer, so a $64$-bit integer should be used.

Solution written by GPT5.5