Given a number N. The task is to write a program to find the N-th term in the below series:

0, 0, 2, 1, 4, 2, 6, 3, 8, 4, 10, 5, 12, 6, 14, 7, 16, 8,…..

**Examples**:

Input : N = 10 Output : 4 Input : N = 7 Output : 6

On observing carefully, you will find that the series is a mixture of 2 series:

- Terms at odd positions in the given series form the series of even numbers in increasing order starting from 0. Like, 0,2,4,6,..
- Terms at even positions in the given series are derived from the previous term using the formula (previousTerm/2). That is, the terms at even positions are half of their previous term.

Now, it is known that every odd positioned term forms an even series starting from 0 and every even positioned term is the half of the previous odd positioned term.

Therefore first check whether the input number N is even or odd. If it is odd, set N=(N/2) + 1(since there are Two series running parallelly) and find the Nth term by using formula 2*(N-1) ( N-1 because the series starts with 0).

Similarly, if N is even, set N = N/2, use the previous formula and divide the answer by 2.

Below is the implementation of above approach:

## C++

`// CPP program to find N-th term` `// in the series` `#include <iostream>` `#include <math.h>` `using` `namespace` `std;` `// Function to find N-th term` `// in the series` `void` `findNthTerm(` `int` `n)` `{ ` ` ` `// If n is even` ` ` `if` `(n % 2 == 0) {` ` ` `n = n / 2;` ` ` `n = 2 * (n - 1);` ` ` `cout << n / 2 << endl;` ` ` `}` ` ` `// If n is odd` ` ` `else` `{` ` ` `n = (n / 2) + 1;` ` ` `n = 2 * (n - 1);` ` ` `cout << n << endl;` ` ` `}` `}` `// Driver code` `int` `main()` `{` ` ` `int` `X = 10;` ` ` `findNthTerm(X);` ` ` ` ` `X = 7;` ` ` `findNthTerm(X);` ` ` ` ` `return` `0;` `}` |

## Java

`// Java program to find N-th term` `// in the series` `// Function to find N-th term` `// in the series` `class` `GFG` `{` `static` `void` `findNthTerm(` `int` `n)` `{` ` ` `// If n is even` ` ` `if` `(n % ` `2` `== ` `0` `)` ` ` `{` ` ` `n = n / ` `2` `;` ` ` `n = ` `2` `* (n - ` `1` `);` ` ` `System.out.println(n / ` `2` `);` ` ` `}` ` ` ` ` `// If n is odd` ` ` `else` ` ` `{` ` ` `n = (n / ` `2` `) + ` `1` `;` ` ` `n = ` `2` `* (n - ` `1` `);` ` ` `System.out.println(n);` ` ` `}` `}` `// Driver code` `public` `static` `void` `main(String args[])` `{` ` ` `int` `X = ` `10` `;` ` ` `findNthTerm(X);` ` ` ` ` `X = ` `7` `;` ` ` `findNthTerm(X);` `}` `}` `// This code is contributed by Subhadeep` |

## Python 3

`# Python 3 program to find N-th term` `# in the series` ` ` `# Function to find N-th term` `# in the series` `def` `findNthTerm(n):` ` ` ` ` `# If n is even` ` ` `if` `(n ` `%` `2` `=` `=` `0` `):` ` ` `n ` `=` `n ` `/` `/` `2` ` ` `n ` `=` `2` `*` `(n ` `-` `1` `)` ` ` `print` `( n ` `/` `/` `2` `)` ` ` `# If n is odd` ` ` `else` `:` ` ` `n ` `=` `(n ` `/` `/` `2` `) ` `+` `1` ` ` `n ` `=` `2` `*` `(n ` `-` `1` `)` ` ` `print` `(n)` ` ` `# Driver code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` `X ` `=` `10` ` ` `findNthTerm(X);` ` ` ` ` `X ` `=` `7` `;` ` ` `findNthTerm(X)` |

## C#

`// C# program to find N-th term` `// in the series` `using` `System;` `// Function to find N-th term` `// in the series` `class` `GFG` `{` `static` `void` `findNthTerm(` `int` `n)` `{` ` ` `// If n is even` ` ` `if` `(n % 2 == 0)` ` ` `{` ` ` `n = n / 2;` ` ` `n = 2 * (n - 1);` ` ` `Console.Write(n / 2);` ` ` `}` ` ` ` ` `// If n is odd` ` ` `else` ` ` `{` ` ` `n = (n / 2) + 1;` ` ` `n = 2 * (n - 1);` ` ` `Console.Write(n);` ` ` `}` `}` `// Driver code` `public` `static` `void` `Main()` `{` ` ` `int` `X = 10;` ` ` `findNthTerm(X);` ` ` `Console.Write(` `"\n"` `);` ` ` `X = 7;` ` ` `findNthTerm(X);` `}` `}` `// This code is contributed` `// by Smitha` |

## PHP

`<?php` `// PHP program to find N-th` `// term in the series` `// Function to find N-th` `// term in the series` `function` `findNthTerm(` `$n` `)` `{` ` ` `// If $n is even` ` ` `if` `(` `$n` `% 2 == 0)` ` ` `{` ` ` `$n` `= ` `$n` `/ 2;` ` ` `$n` `= 2 * (` `$n` `- 1);` ` ` `echo` `$n` `/ 2 . ` `"\n"` `;` ` ` `}` ` ` ` ` `// If $n is odd` ` ` `else` ` ` `{` ` ` `$n` `= (int)(` `$n` `/ 2) + 1;` ` ` `$n` `= 2 * (` `$n` `- 1);` ` ` `echo` `$n` `. ` `"\n"` `;` ` ` `}` `}` `// Driver code` `$X` `= 10;` `findNthTerm(` `$X` `);` ` ` `$X` `= 7;` `findNthTerm(` `$X` `);` ` ` `// This code is contributed` `// by ChitraNayal` `?>` |

## Javascript

`<script>` `// JavaScript program to find N-th term` `// in the series` `// Function to find N-th term` `// in the series` `function` `findNthTerm(n)` `{ ` ` ` `// If n is even` ` ` `if` `(n % 2 == 0) {` ` ` `n = Math.floor(n / 2);` ` ` `n = 2 * (n - 1);` ` ` `document.write(Math.floor(n / 2) + ` `"<br>"` `);` ` ` `}` ` ` `// If n is odd` ` ` `else` `{` ` ` `n = Math.floor(n / 2) + 1;` ` ` `n = 2 * (n - 1);` ` ` `document.write(n + ` `"<br>"` `);` ` ` `}` `}` ` ` `// Driver code` ` ` `let X = 10;` ` ` `findNthTerm(X);` ` ` ` ` `X = 7;` ` ` `findNthTerm(X);` ` ` ` ` `// This code is contributed by Surbhi Tyagi` `</script>` |

**Output:**

4 6

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