[Actually is 5, not 7.]

The first three terms in that long sum will all be equal to 1 (because and both lie between 1 and 2). The next batch of terms, from to will all be equal to 2. Count how many of these terms there are. Then do the same for the batches of terms that are equal to 3, 4, 5, 6. Finally, the last two terms are equal to 7.

Now add all those numbers to get the answer.