#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll,ll> P;
#define REP(i,n) for(ll i=0;i<ll(n);i++)













int main(void){
	cin.tie(nullptr);  ios_base::sync_with_stdio(false);
	ll i,j;
	
	
	
	ll D;
	cin >> D;



	cout << "? " << 0 << endl;
	cout.flush();

	ll a;
	cin >> a;


	cout << "? " << 1 << endl;
	cout.flush();

	ll b;
	cin >> b;


	cout << "! " << b-a << endl;
	cout.flush();





	return 0;

}