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 **N ^{th}** number using Fibonacci rule i.e.

**fib(i) = fib(i – 1) + fib(i – 2)**

**Example:**

Input:A = 2, B = 3, N = 4Output:8

The series will be 2, 3, 5, 8, 13, 21, …

And the 4th element is 8.Input:A = 5, B = 7, N = 10Output:343

**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 <iostream>` `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` |

## Javascript

`<script>` `// javascript implementation of the approach` ` ` `// Function to return the Nth number of` ` ` `// the modified Fibonacci series where` ` ` `// A and B are the first two terms` ` ` `function` `findNthNumber(A , B , N) {` ` ` `// To store the current element which` ` ` `// is the sum of previous two` ` ` `// elements of the series` ` ` `var` `sum = 0;` ` ` `// This loop will terminate when` ` ` `// the Nth element is found` ` ` `for` `(i = 2; i < N; i++) {` ` ` `sum = A + B;` ` ` `A = B;` ` ` `B = sum;` ` ` `}` ` ` `// Return the Nth element` ` ` `return` `sum;` ` ` `}` ` ` `// Driver code` ` ` ` ` `var` `A = 5, B = 7, N = 10;` ` ` `document.write(findNthNumber(A, B, N));` `// This code is contributed by todaysgaurav` `</script>` |

**Output:**

343

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