#include <bits/stdc++.h>
#include <sstream>

//#define int long long
#define endl '\n'
#define IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
typedef long long ll;

using namespace std;

signed main() {
    int n,x,y;
    cin>>n;
    int a=0,aa=0;
    int l=1,r=n;
    while(l<=r) {
    	int x,y;
        printf("? %d\n",l);
        cin>>x;
        if(x==a)
        {
			printf("! %d\n",l);return 0;
		}
		printf("? %d\n",(l+r)/2);
		cin>>y;
		if(y==x)
        {
			printf("! %d\n",(l+r)/2);return 0;
		}
		else if(x<y)
		{
			l=(l+r)/2+1;
		}
		else if(x>y)
		{
			r=(l+r)/2-1;
		}
        a=y;
    }
    printf("! %d",l);
    return 0;
}