The only difference between the easy and the hard version is the limit to the number of queries.

This is an interactive problem.

There is an array $$$a$$$ of $$$n$$$ different numbers. In one query you can ask the position of the second maximum element in a subsegment $$$a[l..r]$$$. Find the position of the maximum element in the array in no more than 20 queries.

A subsegment $$$a[l..r]$$$ is all the elements $$$a_l, a_{l + 1}, ..., a_r$$$. After asking this subsegment you will be given the position of the second maximum from this subsegment in the whole array.

Input

The first line contains a single integer $$$n$$$ $$$(2 \leq n \leq 10^5)$$$ — the number of elements in the array.

Interaction

You can ask queries by printing "? $$$l$$$ $$$r$$$" $$$(1 \leq l \lt r \leq n)$$$. The answer is the index of the second maximum of all elements $$$a_l, a_{l + 1}, ..., a_r$$$. Array $$$a$$$ is fixed beforehand and can't be changed in time of interaction.

You can output the answer by printing "! $$$p$$$", where $$$p$$$ is the index of the maximum element in the array.

You can ask no more than 20 queries. Printing the answer doesn't count as a query.

After printing a query do not forget to output end of line and flush the output. Otherwise, you will get Idleness limit exceeded. To do this, use:

fflush(stdout) or cout.flush() in C++;
System.out.flush() in Java;
flush(output) in Pascal;
stdout.flush() in Python;
see documentation for other languages

Hacks

To make a hack, use the following test format.

In the first line output a single integer $$$n$$$ $$$(2 \leq n \leq 10^5)$$$. In the second line output a permutation of $$$n$$$ integers $$$1$$$ to $$$n$$$. The position of $$$n$$$ in the permutation is the position of the maximum

Note

In the sample suppose $$$a$$$ is $$$[5, 1, 4, 2, 3]$$$. So after asking the $$$[1..5]$$$ subsegment $$$4$$$ is second to max value, and it's position is $$$3$$$. After asking the $$$[4..5]$$$ subsegment $$$2$$$ is second to max value and it's position in the whole array is $$$4$$$.

Note that there are other arrays $$$a$$$ that would produce the same interaction, and the answer for them might be different. Example output is given in purpose of understanding the interaction.

Guessing the Greatest (hard version)

Examples