Related Articles
Given a number x , find y such that x*y + 1 is not a prime
• Last Updated : 21 May, 2021

Given a number x, Find y (y > 0) such that x*y + 1 is not a prime.
Examples:

```Input : 2
Output : 4

Input : 5
Output : 3```

Observation:

x*(x-2) + 1 = (x-1)^2 which is not a prime.

Approach :

`For x > 2, y will be x-2 otherwise y will be x+2`

## C++

 `#include ``using` `namespace` `std;` `int` `findY(``int` `x)``{``    ``if` `(x > 2)``        ``return` `x - 2;` `    ``return` `x + 2;``}` `// Driver code``int` `main()``{``    ``int` `x = 5;``    ``cout << findY(x);``    ``return` `0;``}`

## Java

 `// JAVA implementation of above approach` `import` `java.util.*;` `class` `GFG``{``    ``public` `static` `int` `findY(``int` `x)``    ``{``        ``if` `(x > ``2``)``            ``return` `x - ``2``;``    ` `        ``return` `x + ``2``;``    ``}` `    ``// Driver code``    ``public` `static` `void`  `main(String [] args)``    ``{``        ``int` `x = ``5``;``        ``System.out.println(findY(x));` `    ``}``    ` `}`  `// This code is contributed``// by ihritik`

## Python3

 `# Python3 implementation of above``# approach` `def` `findY(x):` `    ``if` `(x > ``2``):``        ``return` `x ``-` `2``    ` `    ``return` `x ``+` `2` `# Driver code``if` `__name__``=``=``'__main__'``:``    ``x ``=` `5``    ``print``(findY(x))` `# This code is contributed``# by ihritik`

## C#

 `// C# implementation of above approach``using` `System;` `class` `GFG``{``public` `static` `int` `findY(``int` `x)``{``    ``if` `(x > 2)``        ``return` `x - 2;` `    ``return` `x + 2;``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `x = 5;``    ``Console.WriteLine(findY(x));``}``}` `// This code is contributed``// by Subhadeep`

## PHP

 ` 2)``        ``return` `\$x` `- 2;` `    ``return` `\$x` `+ 2;``}` `// Driver code``\$x` `= 5;``echo` `(findY(``\$x``));` `// This code is contributed``// by Shivi_Aggarwal``?>`

## Javascript

 ``

Output:

`3`

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with industry experts, please refer Geeks Classes Live

My Personal Notes arrow_drop_up