#include <iostream>

#define MIN 1
#define	MAX	1000000000

int Center(int lower, int higher)
{
	higher -= lower;
	higher /= 2;

	return lower + higher;
}

int main()
{
	int min = MIN;
	int max = MAX;

	int in;

	for(int i = 0; i < 99; i++)
	{
		int c = Center(min, max);
		std::cout << "? " << c << std::endl;
		std::cout << std::flush;

		std::cin >> in;

		(in == 1)? min = c : max = c - 1;

		if ((max - min) <= 1)
			break;
	}
	
	std::cout << "? " << max << std::endl;
	std::cout << std::flush;
	std::cin >> in;
	
	int ans = (in == 0)? min : max;

	std::cout << "! " << ans << std::endl;

	return 0;
}