Prove that the sum of the first n Fibonacci numbers is equal to the (n+2)nd fibonacci number minus one.

Base case: n=1

1st Fib# =1 =third fib# -1=2-1 True

This is where I have problems.

$\displaystyle f_{1}+f_{2}+f_{3}+....+f_{n}+f_{n+1}$

$\displaystyle =f_{n+2}-1+f_{n+1}$

after this I have no idea how to proceed.