What is the time complexity of following code for calculating nth fibonacci number
long fib(int n){
    if(n == 0 || n == 1){
         return n;
    }
    return fib(n - 1) + fib(n - 2);
}

Options
O(n)
O(n^2)
O(2^n)
O(n^3)


O(2^n)
