Ravi and his binary numbers

In the recent exam a question came based on binary numbers. according to the question you will be given a number N . We all know that we can generate 2^N combinations . Now we have to print the number of good binary numbers in the 2^n combinations A binary number is called good if there no substring '111' else it is bad binary number .since the answer is very large output the answer modulo 10^9+7