#include <iostream>

#define MIN 1
#define	MAX	1000000000

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

	return lower + higher;
}

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

	int in;

	for(int i = 0; i < 100; 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 (min == max)
			break;
	}

	std::cout << min;
}