#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)

using namespace std;

//res[short:-1,long:1,equal:0]
int ask(unsigned long long int X){
    cout << "? " << X << endl;
    unsigned long long int res;
    cin >> res;
    return res;
}

void res(unsigned long long int Y){
    cout << "! " << Y << endl;
    return;
}

int main(){
    unsigned long long int guess = 5*pow(10,8);
    unsigned long long int temp = guess;
    rep(i,100){
        temp = temp/2+pow(-1,i);
        int num = ask(guess);
        if(num == 0){
            res(guess + i);
            break;
        }else{
            guess += num*temp;    
        }  
    }
}