import java.io.PrintStream;
import java.io.PrintWriter;
import java.util.Scanner;


public class Main_yukicoder246 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Printer pr = new Printer(System.out);

        int l = 0;
        int r = 1000000000;
		while (r - l > 1) {
			int mid = (r + l) / 2;
			pr.printf("? %d\n", mid);
			pr.flush();
			int f = sc.nextInt();
			if (f == 0) {
				r = mid;
			} else {
				l = mid;
			}
		}

        System.out.println(l);

        pr.close();
        sc.close();
    }

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}