the series can be expanded as 1-1/2+1/2-1/3...........1/n-1/n+1, all the terms will cancel out each other except first and last term so at the end we will get 1-1/n+1, and for larger N this term will be getting smaller and smaller so when n is very large 1/n+1 will be equal to 0, therefore, the final answer is 1.