#include<stdio.h>
int main()
{
	long long int i;
	long long int x[32], xx;
	long long int min, mid, max;
	min = 0;
	max = 1e6;
	printf("? -100000000\n");
	fflush(stdout);
	x[0] = -1e8;
	long long int res;
	for (xx = 1; max - min > 1; xx++)
	{
		mid = (max + min) / 2;
		x[xx] = 2 * mid - x[xx - 1];
		printf("? %lld\n", x[xx]);
		fflush(stdout);
		scanf("%lld", &res);
		if (res < 0)
			return 0;
		if (x[xx - 1] < min)
		{
			if (res > 0)
				min = mid - 1;
			else
				max = mid;
		}
		else
		{
			if (res == 0)
				min = mid - 1;
			else
				max = mid;
		}
	}
	printf("! %lld\n", max);
	fflush(stdout);
	return 0;
}