You are provided with coins of denominations "a" and "b". You are required to find the least value of n, such that all currency values greater than or equal to n can be made using any number of coins of denomination "a" and "b" and in any order. If no such number exists, print "-1" in that case. how can i solve this question ?

it is a simple problem based on the Chicken McNugget Theorem. You can use the theorem to get your answer. for proves, refer to this link: https://brilliant.org/discussions/thread/chicken-mcnugget-theorem/