Given a number N, evaluate the following expression.
f(n-1)*f(n+1) - f(n)*f(n) where f(n) is the n-th Fibonacci number with n >= 1.
Fibonacci Sequence is 0, 1, 1, 2, 3, 5, 8, 13,… (here 0 is the 0th Fibonacci number)

Your Task:
You do not need to read input or print anything. Your Task is to complete the function fibExpresssion() which takes the value N as input parameters and returns the required difference.

Expected Time Complexity: O(1) Expected Auxiliary Space: O(1)