# Find the previous fibonacci number

Given a Fibonacci number N, the task is to find the previous Fibonacci number.

Examples:

Input: N = 8
Output: 5
5 is the previous fibonacci number before 8.

Input: N = 5
Output: 3

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The ratio of two adjacent numbers in the Fibonacci series rapidly approaches ((1 + sqrt(5)) / 2). So if N is divided by ((1 + sqrt(5)) / 2) and then rounded, the resultant number will be the previous Fibonacci number.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` ` `  `using` `namespace` `std; ` ` `  `// Function to return the previous ` `// fibonacci number ` `int` `previousFibonacci(``int` `n) ` `{ ` `    ``double` `a = n / ((1 + ``sqrt``(5)) / 2.0); ` `    ``return` `round(a); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 8; ` `    ``cout << (previousFibonacci(n)); ` `} ` ` `  `// This code is contributed by Mohit Kumar `

## Java

 `// Java implementation of the approach ` `import` `java.io.*; ` ` `  `class` `GFG ` `{ ` `         `  `// Function to return the previous ` `// fibonacci number ` `static` `int` `previousFibonacci(``int` `n) ` `{ ` `    ``double` `a = n / ((``1` `+ Math.sqrt(``5``)) / ``2.0``); ` `    ``return` `(``int``)Math.round(a); ` `} ` ` `  `// Driver code ` `public` `static` `void` `main (String[] args)  ` `{ ` `    ``int` `n = ``8``; ` `    ``System.out.println(previousFibonacci(n)); ` `} ` `} ` ` `  `// This code is contributed by ajit.  `

## Python3

 `# Python3 implementation of the approach  ` `from` `math ``import` `*` ` `  `# Function to return the previous  ` `# fibonacci number  ` `def` `previousFibonacci(n):  ` `    ``a ``=` `n``/``((``1` `+` `sqrt(``5``))``/``2.0``) ` `    ``return` `round``(a)  ` ` `  `# Driver code  ` `n ``=` `8` `print``(previousFibonacci(n))  `

## C#

 `// C# implementation of the approach ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `// Function to return the previous ` `// fibonacci number ` `static` `int` `previousFibonacci(``int` `n) ` `{ ` `    ``double` `a = n / ((1 + Math.Sqrt(5)) / 2.0); ` `    ``return` `(``int``)Math.Round(a); ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main() ` `{ ` `    ``int` `n = 8; ` `    ``Console.Write(previousFibonacci(n)); ` `} ` `} ` ` `  `// This code is contributed by Akanksha_Rai `

Output:

```5
```

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