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# Fibonacci problem (Value of Fib(N)*Fib(N) – Fib(N-1) * Fib(N+1))

• Last Updated : 10 May, 2021

Given a positive integer N, the task is to find Fib(N)2 – (Fib(N-1) * Fib(N+1)) where Fib(N) returns the Nth Fibonacci number.
Examples:

Input: N = 3
Output:
Fib(3) * Fib(3) – Fib(2) * Fib(4) = 4 – 3 = 1
Input: N = 2
Output: -1
Fib(2) * Fib(2) – Fib(1) * Fib(3) = 1 – 2 = -1

Approach: This question can be approached by first trying out a few test cases. Let’s take a few examples:

For N = 1 : Fib(1) * Fib(1) – Fib(0) * Fib(2) = 1 – 0 = 1
For N = 2 : Fib(2) * Fib(2) – Fib(1) * Fib(3) = 1 – 2 = -1
For N = 3 : Fib(3) * Fib(3) – Fib(2) * Fib(4) = 4 – 3 = 1
For N = 4 : Fib(4) * Fib(4) – Fib(3) * Fib(5) = 9 – 10 = -1
We observe here that when N is even then the answer will be -1 and when the N is odd then the answer will be 1

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `int` `getResult(``int` `n)``{``    ``if` `(n & 1)``        ``return` `1;``    ``return` `-1;``}` `// Driver code``int` `main()``{``    ``int` `n = 3;``    ``cout << getResult(n);``}`

## Java

 `//Java implementation of the approach` `import` `java.io.*;` `class` `GFG {``    ` `static` `int` `getResult(``int` `n)``{``    ``if` `((n & ``1``)>``0``)``        ``return` `1``;``    ``return` `-``1``;``}` `// Driver code``    ``public` `static` `void` `main (String[] args) {``    ` `    ``int` `n = ``3``;``    ``System.out.println(getResult(n));``    ``}``//This code is contributed by @Tushil.   ``}`

## Python3

 `# Python 3 implementation of``# the approach``def` `getResult(n):` `    ``if` `n & ``1``:``        ``return` `1``    ``return` `-``1` `# Driver code``n ``=` `3``print``(getResult(n))` `# This code is contributed``# by Shrikant13`

## C#

 `//C# implementation of the approach` `using` `System;` `class` `GFG {``    ` `static` `int` `getResult(``int` `n)``{``    ``if` `((n & 1)>0)``        ``return` `1;``    ``return` `-1;``}` `// Driver code``    ``public` `static` `void` `Main () {``    ` `    ``int` `n = 3;``    ``Console.WriteLine(getResult(n));``    ``}``//This code is contributed by anuj_67..``}`

## PHP

 ``

## Javascript

 ``
Output:
`1`

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