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Find the Nth element of the modified Fibonacci series
• Difficulty Level : Basic
• Last Updated : 17 Sep, 2019

Given two integers A and B which are the first two terms of the series and another integer N. The task is to find the Nth number using Fibonacci rule i.e. fib(i) = fib(i – 1) + fib(i – 2)

Example:

Input: A = 2, B = 3, N = 4
Output: 8
The series will be 2, 3, 5, 8, 13, 21, …
And the 4th element is 8.

Input: A = 5, B = 7, N = 10
Output: 343

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Intilalize variable sum = 0 that stores sum of the previous two values. Now, run a loop from i = 2 to N and for each index update value of sum = A + B and A = B, B = sum. Then, finally return the sum which is the required Nth element.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;`` ` `// Function to return the Nth number of``// the modified Fibonacci series where``// A and B are the first two terms``int` `findNthNumber(``int` `A, ``int` `B, ``int` `N)``{`` ` `    ``// To store the current element which``    ``// is the sum of previous two``    ``// elements of the series``    ``int` `sum = 0;`` ` `    ``// This loop will terminate when``    ``// the Nth element is found``    ``for` `(``int` `i = 2; i < N; i++) {``        ``sum = A + B;`` ` `        ``A = B;`` ` `        ``B = sum;``    ``}`` ` `    ``// Return the Nth element``    ``return` `sum;``}`` ` `// Driver code``int` `main()``{``    ``int` `A = 5, B = 7, N = 10;`` ` `    ``cout << findNthNumber(A, B, N);`` ` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``import` `java.util.*;`` ` `class` `GFG ``{`` ` `    ``// Function to return the Nth number of``    ``// the modified Fibonacci series where``    ``// A and B are the first two terms``    ``static` `int` `findNthNumber(``int` `A, ``int` `B, ``int` `N) ``    ``{`` ` `        ``// To store the current element which``        ``// is the sum of previous two``        ``// elements of the series``        ``int` `sum = ``0``;`` ` `        ``// This loop will terminate when``        ``// the Nth element is found``        ``for` `(``int` `i = ``2``; i < N; i++)``        ``{``            ``sum = A + B;`` ` `            ``A = B;`` ` `            ``B = sum;``        ``}`` ` `        ``// Return the Nth element``        ``return` `sum;``    ``}`` ` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `A = ``5``, B = ``7``, N = ``10``;`` ` `        ``System.out.println(findNthNumber(A, B, N));``    ``}``} `` ` `// This code is contributed by PrinciRaj1992`

## Python3

 `# Python3 implementation of the approach`` ` `# Function to return the Nth number of``# the modified Fibonacci series where``# A and B are the first two terms``def` `findNthNumber(A, B, N):`` ` `    ``# To store the current element which``    ``# is the sum of previous two``    ``# elements of the series``    ``sum` `=` `0`` ` `    ``# This loop will terminate when``    ``# the Nth element is found``    ``for` `i ``in` `range``(``2``, N):``        ``sum` `=` `A ``+` `B`` ` `        ``A ``=` `B`` ` `        ``B ``=` `sum``     ` `    ``# Return the Nth element``    ``return` `sum`` ` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``A ``=` `5``    ``B ``=` `7``    ``N ``=` `10`` ` `    ``print``(findNthNumber(A, B, N))`` ` `# This code is contributed by Ashutosh450`

## C#

 `// C# implementation of the approach``using` `System;`` ` `class` `GFG ``{`` ` `    ``// Function to return the Nth number of``    ``// the modified Fibonacci series where``    ``// A and B are the first two terms``    ``static` `int` `findNthNumber(``int` `A, ``int` `B, ``int` `N) ``    ``{`` ` `        ``// To store the current element which``        ``// is the sum of previous two``        ``// elements of the series``        ``int` `sum = 0;`` ` `        ``// This loop will terminate when``        ``// the Nth element is found``        ``for` `(``int` `i = 2; i < N; i++)``        ``{``            ``sum = A + B;`` ` `            ``A = B;`` ` `            ``B = sum;``        ``}`` ` `        ``// Return the Nth element``        ``return` `sum;``    ``}`` ` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `A = 5, B = 7, N = 10;`` ` `        ``Console.WriteLine(findNthNumber(A, B, N));``    ``}``}`` ` `// This code is contributed by AnkitRai01`
Output:
```343
```

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