The Fibonacci numbers start with 0 and 1. The 0th Fibonacci number is 0 and the 1st Fibonacci number is 1. From index 2 on, each Fibonacci number is the sum of the two before it.
As a formula, Fn=Fn−1+Fn−2 for n≥2.
Written out up to n=17, the Fibonacci numbers are as follows.
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597
Given n, write a program that computes the sum of the Fibonacci numbers with an odd index, taken from the 0th through the nth. That is the value of F1+F3+F5+⋯ restricted to the terms whose index is at most n.