#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

//int Len, curlen;
int query(int Y) {
	printf("? %d\n", Y); fflush(stdout);
	int c;
	scanf("%d", &c);
	/*
	if(Y < 0 || Y > (int)1e9) {
		cerr << "err" << endl;
	}
	int c = Y == curlen ? 0 : Y > curlen ? -1 : 1;
	-- curlen; amax(curlen, 0);
	*/
	return c;
}

int main() {
	rep(ii, 1) {
//		curlen = Len = rand() % 100 + 10;
		const int X = 80;
		int c0 = query(X);
		int ans = -1;
		if(c0 <= 0) {
			rep(i, X+1) {
				int c = query(0);
				if(c == 0) {
					ans = i + 1;
					break;
				}
			}
		}else {
			int l = 10, u = (int)1e9;
			rep(i, X) {
				int mid = max(0, (l + u) / 2 - i);
				int c = query(mid);
				if(c == 0) { ans = mid + i + 1; break; }
				if(c == 1) {
					l = mid + i + 1;
				}else {
					u = mid + i - 1;
				}
			}
		}
		printf("! %d\n", ans); fflush(stdout);
//		if(ans != Len)
//			cerr << ans << " != " << Len << endl;
	}
	return 0;
}