Easy But Not Peasy

Huh ! you reached this far ! Chef was too surprised to know that you are not a duffer.However,he still doesn't consider you a Genius. To pass the next test, Chef decided to give you another number $X$. This time ,your task is to change it from odd to even and even to odd. However , the odd number you give for even numbers should be one more than it,but the even number you give for odd numbers shou