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

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 <bits/stdc++.h>
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 <stdio.h>

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

<?php
// PHP implementation of above approach
function findY($x)
{
    if ($x > 2)
        return $x - 2;

    return $x + 2;
}

// Driver code
$x = 5;
echo (findY($x));

// This code is contributed
// by Shivi_Aggarwal
?>

Javascript

<script>

// JavaScript implementation of above approach

// Function to check whether it is possible
// or not to move from (0, 0) to (x, y)
// in exactly n steps
function findY(x)
{
    if (x > 2)
        return x - 2;

    return x + 2;
}

// Driver code

var x = 5;
document.write(findY(x));

// This code is contributed by Ankita saini

</script>

Output:

3

Time Complexity: O(1)

Auxiliary Space: O(1)