# Number of ways to choose a pair containing an even and an odd number from 1 to N

Given a number N, the task is to find the number of pairs containing an even and an odd number from numbers between 1 and N inclusive.

**Note:**Order of numbers in the pair does not matter that is (1, 2) and (2, 1) are the same.

**Examples**:

Input: N = 3 Output: 2 The pairs are (1, 2) and (2, 3). Input: N = 6 Output: 9 The pairs are (1, 2), (1, 4), (1, 6), (2, 3), (2, 5), (3, 4), (3, 6), (4, 5), (5, 6).

**Approach:** Number of ways to form the pairs is **(Total number of Even numbers*Total number of Odd numbers)**.

Thus

- if N is even number of even numbers = number of odd numbers = N/2
- if N is odd number of even numbers = N/2 and number of odd numbers = N/2+1

Below is the implementation of the above approach:

## C++

`// C++ implementation of the above approach ` `#include <iostream> ` `using` `namespace` `std; ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `int` `N = 6; ` ` ` ` ` `int` `Even = N / 2 ; ` ` ` ` ` `int` `Odd = N - Even ; ` ` ` ` ` `cout << Even * Odd ; ` ` ` ` ` `return` `0; ` ` ` `// This code is contributed ` ` ` `// by ANKITRAI1 ` `} ` |

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## Java

`// Java implementation of the above approach ` `import` `java.util.*; ` `import` `java.lang.*; ` `import` `java.io.*; ` `class` `GFG{ ` ` ` `// Driver code ` `public` `static` `void` `main(String args[]) ` `{ ` ` ` `int` `N = ` `6` `; ` ` ` ` ` `int` `Even = N / ` `2` `; ` ` ` ` ` `int` `Odd = N - Even ; ` ` ` ` ` `System.out.println( Even * Odd ); ` ` ` `} ` `} ` |

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## Python3

`# Python implementation of the above approach ` `N ` `=` `6` ` ` ` ` `# number of even numbers ` `Even ` `=` `N` `/` `/` `2` ` ` `# number of odd numbers ` `Odd ` `=` `N` `-` `Even ` `print` `(Even ` `*` `Odd) ` |

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## C#

`// C# implementation of the ` `// above approach ` `using` `System; ` ` ` `class` `GFG ` `{ ` ` ` `// Driver code ` `public` `static` `void` `Main() ` `{ ` ` ` `int` `N = 6; ` ` ` ` ` `int` `Even = N / 2 ; ` ` ` ` ` `int` `Odd = N - Even ; ` ` ` ` ` `Console.WriteLine(Even * Odd); ` `} ` `} ` ` ` `// This code is contributed ` `// by Akanksha Rai(Abby_akku) ` |

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## PHP

`<?php ` `// PHP implementation of the ` `// above approach ` ` ` `// Driver code ` `$N` `= 6; ` ` ` `$Even` `= ` `$N` `/ 2 ; ` ` ` `$Odd` `= ` `$N` `- ` `$Even` `; ` ` ` `echo` `$Even` `* ` `$Odd` `; ` ` ` `// This code is contributed ` `// by ChitraNayal ` `?> ` |

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**Output:**

9

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