#include <bits/stdc++.h>

using namespace std;

int n;

int main() {
	scanf("%d",&n);
	int st = 1, dr = n,last = 1;
	while(dr-st >= 0) {
		int mid = (st+dr)/2;
		printf("? %d\n",mid);
		fflush(stdout);
		int x;
		scanf("%d",&x);
		if(x){
			last = mid;
			dr = mid - 1;
		}else{
			st = mid + 1;
		}
	}
	printf("! %d\n",last);
	fflush(stdout);
	
	return 0;
}