# Given a number x , find y such that x*y + 1 is not a prime

• Last Updated : 08 Mar, 2022

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;``}`

## C

 `#include ` `int` `findY(``int` `x)``{``    ``if` `(x > 2)``        ``return` `x - 2;`` ` `    ``return` `x + 2;``}`` ` `// Driver code``int` `main()``{``    ``int` `x = 5;``    ``printf``(``"%d"``,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`

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