ক্রমিক সংখ্যার গ্যাঁড়াকল | Math Problem

Click here to read the complete problem statement.

Can anyone help me with it

Remember there are also negative integers and when you subtract a negative number that means you are adding that.
Example: 1-(-1)
= 1+1
= 2

But why nagetive integer come ?

if there is not neg int then how the sum is 1010 where numbers are 2020