Program to find Nth odd Fibonacci Number

Given an integer N. The task is to find the N^th odd Fibonacci number.
The odd number fibonacci series is as: 

1, 1, 3, 5, 13, 21, 55, 89, 233, 377, 987, 1597………….and so on.
Note: In the above series we have omitted even terms from the general fibonacci sequence. 

Examples:

Input: N = 3
Output: 3

Input: N = 4
Output: 5

Approach:
On observing carefully, it can be deduced that every third Fibonacci number is even, so the N^th odd Fibonacci number is the {(3*N+1)/2}^th term in the general Fibonacci sequence.
Below is the implementation of the above approach: 

C++

// C++ program for Nth odd fibonacci number

#include <bits/stdc++.h>
using namespace std;

// Function to find nth odd fibonacci number
int oddFib(int n)
{
    n = (3 * n + 1) / 2;
    int a = -1, b = 1, c, i;
    for (i = 1; i <= n; i++) {
        c = a + b;
        a = b;
        b = c;
    }
    return c;
}

// Driver Code
int main()
{
    int n = 4;

    cout << oddFib(n);

    return 0;
}

Java

// Java program for Nth odd fibonacci number
class GFG
{

    // Function to find nth odd fibonacci number
    static int oddFib(int n)
    {
        n = (3 * n + 1) / 2;

        int a = -1, b = 1, c = 0, i;

        for (i = 1; i <= n; i++)
        {
            c = a + b;
            a = b;
            b = c;
        }
        return c;
    }

    // Driver Code
    public static void main (String[] args)
    {
        int n = 4;

        System.out.println(oddFib(n));
    }
}

// This code is contributed by AnkitRai01

Python3

# Python3 program for Nth odd fibonacci number

# Function to find nth odd fibonacci number
def oddFib(n):
    n = (3 * n + 1) // 2

    a = -1
    b = 1
    c = 0
    for i in range(1, n + 1):
        c = a + b
        a = b
        b = c

    return c

# Driver Code
n = 4

print(oddFib(n))

# This code is contributed by mohit kumar

C#

// C# program for Nth odd fibonacci number
using System;

class GFG
{

    // Function to find nth odd fibonacci number
    static int oddFib(int n)
    {
        n = (3 * n + 1) / 2;

        int a = -1, b = 1, c = 0, i;

        for (i = 1; i <= n; i++)
        {
            c = a + b;
            a = b;
            b = c;
        }
        return c;
    }

    // Driver Code
    public static void Main (String[] args)
    {
        int n = 4;

        Console.WriteLine(oddFib(n));
    }
}

// This code is contributed by 29AjayKumar

Javascript

<script>

// JavaScript program for Nth odd fibonacci number

// Function to find nth odd fibonacci number
function oddFib(n)
{
    n = (3 * n + 1) / 2;
    var a = -1, b = 1, c, i;
    for (i = 1; i <= n; i++) {
        c = a + b;
        a = b;
        b = c;
    }
    return c;
}

// Driver Code
var n = 4;
document.write(oddFib(n));

</script>

Output:

5

Time Complexity: O(N)

Auxiliary Space: O(1)