Find the Nth element of the modified Fibonacci series

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 = 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 
 

Approach: Initialize 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: 
 

343

Time Complexity: O(N)

Auxiliary Space: O(1)