#include<bits/stdc++.h>
using namespace std;
int n,res,l,r,mid,tmp,tt;
int main(){
    cin>>n;r=n;l=1;mid=(l+r)/2;
    while(r!=l){
        printf("? %d\n",mid);
        scanf("%d",&tt);
        if(tt==tmp){
            printf("! %d\n",mid);return 0;
        }
        else if(tt==tmp+1){
            tmp=tt;l=mid+1;
        }
        else{
            tmp=tt;r=mid-1;
        }
    }
    printf("! %d\n",r);
    return 0;
}