Problem: 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 ≤ n ≤ 10^5) — the number of elements in the array.

Interaction

You can ask queries by printing "? l r" (1 ≤ l < r ≤ 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 ≤ n ≤ 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

Example

Input


5

3

4



Output


? 1 5

? 4 5

! 1

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.

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
#define int long long
using namespace std;

int query(int l, int r)
{
    if (l >= r)
        return -1;
    cout << "? " << l << " " << r<< endl;
    int i;
    cin >> i;
    return i;
}

void solve()
{
    int n;
    cin >> n;
int ans;
    int smax = query(1,n);
    if (query(1, smax) == smax)
    {
        int l=1,r=smax-1;
        while(l<=r)
        {
            int mid= (l+r)/2;
            if(query(mid,smax)==smax)
            {
                ans=mid;
                l=mid+1;
            }
            else{
                r=mid-1;
            }
        }
    }
    else
    {
         int l=smax+1,r=n;
        while(l<=r)
        {
            int mid= (l+r)/2;
            if(query(smax,mid)==smax)
            {
                ans=mid;
                r=mid-1;
            }
            else{
                l=mid+1;
            }
        }
    }

    cout << "! " << ans << endl;
}

signed main()
{
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}