import java.util.*;
public class candle{
	public static void main(String... args){
		int l = 80,r=100000000;
		if(ask(80) == 0){
			System.out.println("! "+80);
			return;
		}
		if(ask(80)<0){
			for(int i = 2; i <= 100; i++){
				if(ask(0)==0){
					System.out.println("! "+(i-1));
					return;
				}
			}
		}
		int a = 1;
		while(true){
			int b = (l+r)/2;
			if(ask(b-a)==0){
				System.out.println("! "+b);
				return;
			}
			a++;
			if(ask(b-a)>0){
				l=b+1;
			}else{
				r=b;
			}
			if(l>=r)break;
		}
		System.out.println("! "+l);
	}
	public static int ask(long y){
		System.out.println("? "+y);
		Scanner scan = new Scanner(System.in);
		return scan.nextInt();
	}
}