#include <bits/stdc++.h>
using namespace std;
#define rep(i, d, u) for(int i = d; i <= u; ++i)
#define dep(i, u, d) for(int i = u; i >= d; --i)
#define cep(n) while(n--)
#define gep(i, a) for(int i = firs[a]; i; i = neig[i])
int ured() {
	int re = 0;
	char ch;
	do {
		ch = getchar();
	} while('9' < ch || ch < '0');
	do {
		re = re * 10 + (ch ^ '0');
	} while('0' <= (ch = getchar()) && ch <= '9');
	return re;
}
void uwit(int da) {
	int ch[21], cn = 0;
	do {
		ch[++cn] = da - da / 10 * 10;
	} while(da /= 10);
	do {
		putchar('0' ^ ch[cn]);
	} while(--cn);
}
const int _maxn = 1000011;
int n, efle, efri, efmi, efan, lans, rans, tans, latp = 1;
bool visi[_maxn];
int quer(int at) {
	putchar('?'), putchar(' '), uwit(at), putchar('\n'), fflush(stdout), visi[at] = 1;
	return ured();
}
int main() {
	n = ured(), efle = 1, efri = n;
	while(efle <= efri) {
		efmi = efle + efri >> 1;
		if((lans = quer(efmi)) == tans) {
			putchar('!'), putchar(' '), uwit(efmi), putchar('\n'), fflush(stdout);
			return 0;
		}
		while(visi[latp]) {
			++latp;
		}
		if((rans = quer(latp)) == lans) {
			putchar('!'), putchar(' '), uwit(latp), putchar('\n'), fflush(stdout);
			return 0;
		}
		if(lans == rans) {
			if(latp < efmi) {
				efle = latp + 1, efri = efmi - 1;
			} else {
				efle = efmi + 1, efri = latp - 1;
			}
		} else {
			efle = efmi + 1;
		}
		tans = rans;
	}
	return 0;
}